Hammer CLI

It should be possible using hammer to remove the association between a hostgroup and an environment. This is possible in the UI and causes the HG to inherit the environment from a parent HG.

Currently all validation checks fail when trying to unset this value using hammer...

1. hammer hostgroup update --name db --environment-id
   Could not update the hostgroup:
   Error: option '--environment-id': numeric value is required

   See: 'hammer hostgroup update --help'

1. hammer hostgroup update --name db --environment ''
   Could not update the hostgroup:
   Error: environment not found