Patch `salt.utils.which` to fix Django tests.

After the check added in 8deefc16, the django salt module integration test cases started to fail if the django administration script was not found in `$PATH`.
Hide `_infinitedict` from salt's loader.
Merge pull request #7620 from s0undt3ch/hotfix/jenkins

Patch `salt.utils.which` to fix Django tests.