Test case `cli_quit` hang

[abitmore]

Bug Description

Reported in #2204 (comment) and then #2204 (comment), cli_test occasionally hang after finished running the cli_quit test case, with some messages or no message at all. Replacing canceled_exception with a new exception doesn't fix it. I guess the issue is related to exception handling in task management in FC. Probably #2076 will make it obsolete.

Testing wallet connection and quit command.
1435490ms th_a       wallet_api_impl.cpp:168       quit                 ] Quitting Cli Wallet ...
/bts/tests/cli/main.cpp(364): info: check 'exception fc::canceled_exception is caught' passed
Cleanup cli_wallet::boost_fixture_test_case
1435491ms th_a       db_management.cpp:243         close                ] Rewinding from 0 to 0
1435513ms th_a       database_api.cpp:91           ~database_api_impl   ] freeing database api 163935040
1435513ms th_a       database_api.cpp:91           ~database_api_impl   ] freeing database api 163975424
1435513ms th_a       database_api.cpp:91           ~database_api_impl   ] freeing database api 163986128
1435513ms th_a       database_api.cpp:91           ~database_api_impl   ] freeing database api 163970032
1435513ms th_a       database_api.cpp:91           ~database_api_impl   ] freeing database api 163978432
1435514ms p2p        thread.cpp:258                exec                 ] thread canceled: 9 canceled_exception: Canceled

    {}
    p2p  thread_d.hpp:493 start_next_fiber
unknown location(0): fatal error in "cli_quit": memory access violation at address: 0x00000000: no mapping at fault address
/bts/tests/cli/main.cpp(364): last checkpoint
Test is aborted
Leaving test case "cli_quit"; testing time: 64241mks
Leaving test suite "Test Application"

*** 1 failure detected in test suite "Test Application"

Testing wallet connection and quit command.
1062625ms th_a       wallet_api_impl.cpp:168       quit                 ] Quitting Cli Wallet ...
/bts/tests/cli/main.cpp(364): info: check 'exception fc::canceled_exception is caught' passed
Cleanup cli_wallet::boost_fixture_test_case
1062626ms th_a       db_management.cpp:243         close                ] Rewinding from 0 to 0
1062645ms th_a       database_api.cpp:91           ~database_api_impl   ] freeing database api 160498176
1062645ms th_a       database_api.cpp:91           ~database_api_impl   ] freeing database api 160538688
1062645ms th_a       database_api.cpp:91           ~database_api_impl   ] freeing database api 160549264
1062645ms th_a       database_api.cpp:91           ~database_api_impl   ] freeing database api 160533296
1062645ms th_a       database_api.cpp:91           ~database_api_impl   ] freeing database api 160541696
1062646ms p2p        thread.cpp:258                exec                 ] thread canceled: 9 canceled_exception: Canceled

    {}
    p2p  thread_d.hpp:493 start_next_fiber

Testing wallet connection and quit command.
226674ms th_a       wallet_api_impl.cpp:168       quit                 ] Quitting Cli Wallet ...
/bts/tests/cli/main.cpp(364): info: check 'exception fc::cli_quit_exception is caught' passed
Cleanup cli_wallet::boost_fixture_test_case
226675ms th_a       db_management.cpp:243         close                ] Rewinding from 0 to 0
226699ms th_a       database_api.cpp:91           ~database_api_impl   ] freeing database api 146940560
226700ms th_a       database_api.cpp:91           ~database_api_impl   ] freeing database api 146981072
226700ms th_a       database_api.cpp:91           ~database_api_impl   ] freeing database api 146991648
226701ms th_a       database_api.cpp:91           ~database_api_impl   ] freeing database api 146975680
226701ms th_a       database_api.cpp:91           ~database_api_impl   ] freeing database api 146984080
226702ms p2p        thread.cpp:258                exec                 ] thread canceled: 9 canceled_exception: Canceled

    {}
    p2p  thread_d.hpp:493 start_next_fiber
unknown location(0): fatal error in "cli_quit": memory access violation at address: 0x00000000: no mapping at fault address
/bts/tests/cli/main.cpp(364): last checkpoint
Test is aborted
Leaving test case "cli_quit"; testing time: 71191mks
Leaving test suite "Test Application"

*** 1 failure detected in test suite "Test Application"

Impacts
Describe which portion(s) of BitShares Core may be impacted by this bug. Please tick at least one box.

• API (the application programming interface)
• Build (the build process or something prior to compiled code)
• CLI (the command line wallet)
• Deployment (the deployment process after building such as Docker, Travis, etc.)
• DEX (the Decentralized EXchange, market engine, etc.)
• P2P (the peer-to-peer network for transaction/block propagation)
• Performance (system or user efficiency, etc.)
• Protocol (the blockchain logic, consensus, validation, etc.)
• Security (the security of system or user data, etc.)
• UX (the User Experience)
• Other (please add below)

Steps To Reproduce

Run cli_test repeatedly hundreds of times.

Expected Behavior

No error.

Host Environment

• Host OS: Ubuntu 16.04 LTS
• Host Physical RAM 16GB
• BitShares Version: develop
• OpenSSL Version: 1.0.2
• Boost Version: 1.58

CORE TEAM TASK LIST

• Evaluate / Prioritize Bug Report
• Refine User Stories / Requirements
• Define Test Cases
• Design / Develop Solution
• Perform QA/Testing
• Update Documentation