don't call out to prohibitively expensive getRootLoggerName in getLogger, just use 'root' instead

[boegel]

The calls to getRootLoggerName are very expensive when __debug__ is True, since then it relies heavily on Python's inspect module.

For some reason unclear to me, the easyconfig tests that run in GitHub CI with Python 3.6 and 3.7 trigger the path that corresponds with __debug__ being False, despite running under python -O (and also defining $PYTHONOPTIMIZE doesn't help).

Regardless, I think it's fine to strip out the call to getRootLoggerName and just use a fixed 'root' name instead.

For normal use of EasyBuild via the eb command, this doesn't make a difference (since then python -O is used under the covers, and the name of the root logger isn't actually visible anywhere by default unless the %(name)s template is used in the log format set via setLogFormat).

This minor change will significantly speed up the easyconfig tests though, when getRootLoggerName follows the path to inspect...

[boegel]

Some more details: currently ~65% of the time running the easyconfig test suite in GitHub CI with Python 3.6 and 3.7 is spent in getRootLoggerName, so replacing the call with a hardcoded string value is going to result in cutting the test time in half (more even)...

[boegel]

close/re-open to wake up the Hound...

[akesandgren]

LGTM

[akesandgren]

Going in, thanks @boegel!