Avoid redundant include
Extract VersionNumber class

Signed-off-by: Jeffrey Peckham <peckham@pivotallabs.com>
Moved VersionNumber class to bosh_common gem

[#52483555]

Signed-off-by: Chris Brown <cbrown@pivotallabs.com>
Unify and remove the VersionCalc mixin

[finishes #52483555]

The VersionCalc mixin and the associated logic spread around the
director and cli codebases was demanding to be refactored into a class
to encapsulate everything.

* Move complex next rebase version logic into its own class.

Signed-off-by: Jeffrey Peckham <peckham@pivotallabs.com>
Improve the snapshots error logging

[finishes #52569689]

Signed-off-by: Jeffrey Peckham <peckham@pivotallabs.com>