(CPR-52) Add support for the automatic building of nightly signed repos

This PR defines a small stack of rake tasks that handle the signing and shipping of repos for a nightly repo. In the process several rake tasks were moved into the appropriate libraries and some additional utilities were added. This PR also deprecates the gpg_name config setting in favor of the gpg_key, and adds a new signing_server config setting for use in automatic signing.
I'm not sure how far down this rabbit hole its worth going, but if for some reason this method gets called prior to repos existing, it will fail pretty hard on this chdir. Maybe a quick check to make sure the subdirectories exist that we're chdir'ing into?