make ModulesTool a singleton, use 'module use/unuse' rather than fiddling with $MODULEPATH, use $LMOD_QUIET rather than $LMOD_EXPERT
fix deprecation message in systemtools.py
fix unit tests now that ModulesTool is a singleton and use/unuse should be used
purge out any loaded modules before each test

Conflicts:
	test/framework/modules.py
clean up purging on modified $MODULEPATH in modulestool.py unit test module

Conflicts:
	test/framework/modulestool.py
purge *after* setting $MODULEPATH
also enable $LMOD_EXPERT, still requires with Lmod version prior to 5.6
don't run 'module update', there's no need to
improvde debug logging for module command (show all the output)
Merge pull request #944 from boegel/modules_singleton

make ModulesTool a singleton, use 'module use/unuse' rather than fiddling with $MODULEPATH, use $LMOD_QUIET rather than $LMOD_EXPERT