Provide flags to make loader aware of an initial load

If this is the first load of modules (i.e. salt-call) or minion start,
we don't need to reload submodules. This will save some stats and allow
us to further optimize the loader for scenarios where quick loading is
essential.

Conflicts:
	salt/loader.py
	salt/minion.py
Merge pull request #17293 from cachedout/loader_initial

 Provide flags to make loader aware of an initial load