nsxv_cleanup and nsxv3_cleanup scripts are called by unstack.sh and
removes all backend resources, even resources which may have been
created by other devstack deployments using the same backend.
This patch fix this issue, when calling 'unstack.sh' the script will
only remove backend resources that have db record, if 'clean.sh' is
called, then previous behavior is used and all backend resources created
by openstack are removed.
To run the scripts manually, in such way that only backend resources
with db records are cleaned, one must specify '--db-connection' (e.g -
iniget /etc/neutron/neutron.conf database connection) option so the script can
query the DB.
When '--db-connection' option is not specified then all
backend resources are cleaned.
Change-Id: I2283bdb2758c303a46574296e0067f458a6eefcf
3d24d19309