Remove ReST syntax from salt.utils.is_true

This function won't have its docstring parsed to be displayed in the
docs, so it doesn't need fancypants ReST directives.
Add salt.utils.test_mode

This is the first step in making "test" mode for states
case-insensitive. See #3363.
Slight docstring tweak
Handle ints/floats properly in salt.utils.is_true
Make test mode case-insensitive for state module

This implements #3363 for state.sls, state.highstate, state.single, etc.
Fix exception handling
Merge pull request #4237 from terminalmage/issue3363

Add salt.utils.test_mode