Add multi-region support

If only one region is available then the Neutron CLI will just pick the
only one available.  However, if more than one is available, then it
will error out about ambiguous region.  This patch extends the base
provider code to parse out the nova_region_name when it's parsing out
the keystone credentials and define the OS_REGION_NAME environment
variable when calling neutron, if the nova_region_name variable exists
in the config file.

Closes-Bug: #1329552
Change-Id: Ic0d59dcb02a11e93e8fad1e0e2ea830fb0dcccc7
(cherry picked from commit d1235d762b96e36b67180ee06929e36c81efd617)
Set default metadata backlog to 4096

We already optimize the metadata agent by running it in multi-workers,
we need by default to set the metadata backlog value.
Inspired from 19:34: https://www.youtube.com/watch?v=AF9r_VQrcJ0
and https://review.openstack.org/#/c/95372

Change-Id: I68f3414ef56290ca27d11f8cf26febc100741d46
Signed-off-by: Emilien Macchi <emilien.macchi@enovance.com>
(cherry picked from commit 1055a125eb767d08028ab9818e4bbc2fb0009303)
Merge "Add multi-region support" into stable/icehouse
Merge "Set default metadata backlog to 4096" into stable/icehouse