labs: reformat osbash.sh usage text
labs: reformat osbash.sh usage text

This patch reformat the usage text for osbash.sh to (hopefully) be more
readable, more accurate, and to make space for a new option to be added
in a later patch. Also adds "--help" option as an alternative for "-h".

Change-Id: I7c41030ab988b27100c313f3242bf45794b87aa2

openstack/training-labs,dguitarbite/OpenStack-Labs,dguitarbite/OpenStack-Labs,openstack/training-labs,openstack/training-labs,dguitarbite/OpenStack-Labs