DEFAULT_VOLUME_GROUP_NAME volume group is LVM ephemeral storage used by
Nova. It is created by init_nova() if user sets NOVA_BACKEND to "LVM".
However, init_cinder() is also hardcoded to create it, based on the
asumption that CINDER_ENABLED_BACKENDS includes it. That assumption
doesn't hold for the current code. What's more important, even if user
wants to use DEFAULT_VOLUME_GROUP_NAME as one of cinder backends and
adds it to CINDER_ENABLED_BACKENDS, the current code in init_cinder()
are general enough and should work fine. This change removes relevant
code in init_cinder(). It also moves DEFAULT_VOLUME_GROUP_NAME clean-up
code from unstack.sh to cleanup_nova().
Change-Id: I53762f8eda6256f962cc4e1f1098406879bbcf5c
63beab5243