(maint) Split out acceptance and unit test gems in a better way

We want to avoid installing all of the unit test gems when running acceptance.
This patch moves rake into its own place so we can use --without test properly.

Signed-off-by: Ken Barber <ken@bob.sh>
Merge pull request #1026 from kbarber/maint/master/fixup-gemfile-for-acceptance

(maint) Split out acceptance and unit test gems in a better way