Add createJob(unique: true) for fan-out dedup #2230

Job	Run time
testsuite (8.5, sqlite)	28s
testsuite (8.2, sqlite, prefer-lowest)	33s
testsuite (8.2, mysql)	55s
testsuite (8.2, sqlite)	33s
testsuite (8.5, mysql)	1m 2s
testsuite (8.2, pgsql)	53s
testsuite (8.5, pgsql)	48s
Coding Standard & Static Analysis	29s
	5m 41s

Provide feedback