Correct grammar in trove CLI help
Correct grammar in trove CLI help

Fixed grammar errors such as 'a instance' and 'the instance' to be
'an instance.'

Change-Id: I43eb9562c5290d23a0def31249d6c7aefd5dc593
Closes-Bug: #1316307

openstack/python-troveclient,openstack/python-troveclient,Tesora/tesora-python-troveclient,Tesora/tesora-python-troveclient