Use pbr entry_points to setup the cinder scripts

The following patch changes how cinder scripts are
installed and unit tested. This patch moves all the
cinder scripts from bin into cinder/cmd and creates
entry_points for those scripts in setup.cfg. When
cinder is installed, these scripts will be installed
under /usr/local/bin by pbr.

DocImpact: 'host' config option for multiple-storage backends
in cinder.conf is renamed to 'backend_host' in order to avoid
a naming conflict with the 'host' to locate redis
Change-Id: If82cf0c58d765bf79dbf721ca95c10a468940cab
Implements: blueprint unit-test-cases-for-cinder-scripts
Merge "Use pbr entry_points to setup the cinder scripts"