Switch to pre-versioning to match neutron version
Switch to pre-versioning to match neutron version

Starting from liberty, date-based versions will no longer be used
for Neutron. See commit 2db459f284002e45497d768a8a53c9b43d045d45
for more details.

This patch changes bsnstacklib to follow the same semantics to avoid
confusion about mappings between versions.

In the commit immediately before this one, a 7.0.0 tag was pushed up
for PBR to start calculating the previous version from.
http://docs.openstack.org/developer/pbr/#version

Change-Id: Ic2ae631ec86fa9858c78e0087fa3392b17cd3032

openstack/networking-bigswitch,stackforge/networking-bigswitch,wolverineav/networking-bigswitch,wolverineav/networking-bigswitch,stackforge/networking-bigswitch,openstack/networking-bigswitch