Fix test.py so it runs all doctests

Also fixes some of broken doctests.
Merge branch 'master' into fix-broken-doctests

Conflicts:
	pynag/Model/__init__.py
	pynag/Plugins/__init__.py
More doctest fixes
Replace importlib.import_module with __import__

importlib is not supported on all architectures (namely travis)
Remove unusued python files
Refactor PerfdataMetrics.split_value_and_uom()

It is now a module level function so it can be used
universally outside of perfdatametrics.

Conflicts:
	pynag/Plugins/relational_thresholds.py
	pynag/Utils/metrics.py
Merge branch 'master' into fix-broken-doctests-merge

Conflicts:
	pynag/Plugins/__init__.py
Merge pull request #199 from pynag/fix-broken-doctests

Fix broken doctests
Merge branch 'master' into relational-operators-v3