Move __salt__['config.is_true'] to salt.utils

This function doesn't need to interact with the rest of the modules, so
it fits better in salt.utils.
Fix refs to __salt__['config.is_true']
Make rh_service.py properly support upstart

This fixes #3183.
Merge pull request #4227 from terminalmage/issue3183

 Move config.is_true, make upstart work properly in rh_service.py