Add setting of placement microversion on tempest conf
Add setting of placement microversion on tempest conf

Tempest not support placement microversion setting so that
test can call APIs with specific placement microversion.

This commit adds the setting of placement API microversion on
Tempest conf.

Change-Id: Ie04aa993ec7a1495740d9267b076a40f4291e25e

nawawi/openstack,openstack-dev/devstack,openstack-dev/devstack,dtroyer/devstack,nawawi/openstack,dtroyer/devstack