Mention 2.51 in help for openstack server event show
Mention 2.51 in help for openstack server event show

With the 2.51 compute API microversion, non-admin users can also
see event details for a given request. This change mentions that
in the help text for "openstack server event show".

While in here, change the _info private attribute access to the
to_dict() usage.

Change-Id: I5fd487b17c4b85bd7e619112ad262ffdd3a940c8
Task: 21199
Story: 2002193

dtroyer/python-openstackclient,openstack/python-openstackclient,openstack/python-openstackclient,dtroyer/python-openstackclient