replace pexpect calls with direct function call and exec while preserving the original logic

<!--
    Please make sure you've read and understood our contributing guidelines:
    https://github.com/Azure/SONiC/blob/gh-pages/CONTRIBUTING.md

    ** Make sure all your commits include a signature generated with `git commit -s` **

    If this is a bug fix, make sure your description includes "closes #xxxx",
    "fixes #xxxx" or "resolves #xxxx" so that GitHub automatically closes the related
    issue when the PR is merged.

    If you are adding/modifying/removing any command or utility script, please also
    make sure to add/modify/remove any unit tests from the tests
    directory as appropriate.

    If you are modifying or removing an existing 'show', 'config' or 'sonic-clear'
    subcommand, or you are adding a new subcommand, please make sure you also
    update the Command Line Reference Guide (doc/Command-Reference.md) to reflect
    your changes.

    Please provide the following information:
-->

#### What I did
streamlined the picocom launch process

#### How I did it
replaced the first pexpect call with a direct function call
wrapped the picocom launch in a bash script
replaced the second pexpect call with execvp

#### How to verify it
first, launch console app just like before
then, use ps -ef to make sure "connect line" is no longer a standalone process

#### Previous command output (if the output of a command-line utility has changed)
connect line X or just reverse ssh

Signed-off-by: Sonic Build Admin <sonicbld@microsoft.com>