v7: Align restart behavior with push & restage

- During a non-rolling restart, `cf restart` would previously ignore the
no-wait flag. This is inconsistent with the behavior of `cf push` and
now `cf restage`.
- This commit ensures that `cf restart` respects the value of the no-wait
flag, whether or not the deployment strategy is set to rolling.
- This commit also makes helper methods in the restart command private
since they are not used elsewhere.

[#169413098]

Co-authored-by: Belinda Liu <bliu@pivotal.io>