Create a monasca group

All monasca users will belong to the monasca group so
/var/log/monasca can be writable for all monasca users so there can
be the one monasca log directory

There will no longer be a monasca-notification group

The code adding this group will be added to other cookbooks so the group
will be created correctly no matter which cookbook runs first

Change-Id: Ic47701fa24d33a8d8d713697901f13c09790c87d