Allow moduli to be pulled as file

[pepoluan]

My patch allows the 'moduli' to be pulled as a file instead of specified literally in the pillar.

I made this patch because:

• Inlining tens of lines of moduli into a pillar file is neither fun nor tidy
• Some paranoid people might be regenerating the moduli file periodically; this patch allows them to simply regenerate the moduli file directly into the Salt fileserver / webserver location

[gravyboat]

This is a good change, thanks!

[pepoluan]

Yay! Thanks!