Define and use TIMEOUT_LOG_PREFIX in log for timeout tests
Extend LogHandler test class to extract timeout values

Also added a test of LogHandler class.
Assert that all timeouts in API tests are default value
Use symbolic reference instead of hard coded string
Test timeout in fetch()
Only construct timeout expectations array if timeout is visible
Set timeout on clone_()
Add timeout test for submodule update
Implement timeout on checkout as progress towards [FIX JENKINS-22400]

Does not complete the fix of JENKINS-22400 because the git plugin
needs to call the newly added timeout() method.

Does not complete the [FIX JENKINS-20387] because it has not yet added
timeout to clean.