Begin systemizing files in pkg/registry

Files that have RESTStorage implementations now end in "storage", and
files that have registries now end in "registry". I removed some
underscores in file names, since it seems to be go style not to have
them. I split minion_registry.go into two files.

We should consider splitting this package into two, to make more clear
the separation between the layers.
Extract "pkg/version".PrintAndExitIfRequested() to its own package
because it causes a runtime panic if a binary which has its own implementation
of "-version" flag tries to reuse a package library which indirectly depend on
"pkg/version".

e.g. If such an user-defined binary tires to link "pkg/api" or "pkg/client",
the binary fails with a runtime panic "flag redefined: version".
Disable curl progress bar when running vagrant up
Merge pull request #733 from mfojtik/vagrant_silent

Disable curl progress bar when running vagrant up
Merge pull request #731 from yugui/fix/flag-panic

Extract "pkg/version".PrintAndExitIfRequested() to its own package
Merge pull request #730 from lavalamp/rename

Begin systemizing files in pkg/registry