Add workaround for horizon image upload issue

Add workaround for horizon image upload issue

JIRA: COMPASS-573

1. With HORIZON_IMAGES_UPLOAD_MODE set to direct
Horizon provides the endpoint for Glance based on
OPENSTACK_ENDPOINT_TYPE. If OPENSTACK_ENDPOINT_TYPE
is set to internalURL any browser outside the internal
network is unable to upload image. Add ansible task to
set HORIZON_IMAGES_UPLOAD_MODE to legacy as a workaround.

2. Add ansible lookup plugin to get openstack release

3. set openstack_release into group_vars/all in config-osa
to make this variable readable for other tasks

Change-Id: I9ef358e1f4acb0c329a032e18359de12284f3b56
Signed-off-by: Harry Huang <huangxiangyu5@huawei.com>