Separate "prepare cf" and "cf help"

Dedicated, ordered command classes & specs
Use Command#director directly instead of renaming

director_client was more clear as to what it was; but let's
go with the superclass method name
clean out cf_help spec
Extract latest release number in spec into variable
prepare cf --release-version 132

Support:
* --release-version v132
* --release-version 132
prepare cf - only upload stemcell if none exist
list_releases returns different value than expected
Merge pull request #198 from cloudfoundry-community/separate_commands

Only upload release if missing; stemcell if none exists