Usage of a weighted loadfactor in puppetmaster

This allows for a more fine tuned distribution of load to backend
puppetmasters through mod_proxy's loadfactor attribute. This is exposed
to class callers via converting the workers parameter to a hash.

Change-Id: I2ba49b278af428da7e390c2b75ad11f04d022420
Merge "Usage of a weighted loadfactor in puppetmaster" into production