Implement finding by name

tuskar overcloud-{show,delete,update} and
tuskar overcloud-role-{show,delete,update}
now work by specifying the name, not just by id.

If the find_resource method can not find the entity by id or uuid, it gets
the list of entities and looks it up by name.

The do_overcloud_show, do_overcloud_update, do_overcloud_delete and
do_overcloud_role_show, do_overcloud_role_update, do_overcloud_role_delete
methods have also been modified to reflect the changes.

Added unittest for find_resource and updated the existing unittests.

Change-Id: I053d26ca5a6ce727c77863c7f7a4ebfa0687a497
Closes-Bug: #1308173
Merge "Implement finding by name"