Apply image location selection strategy

Apply image location selection strategy into Glance server side. Image
download handling and "direct URL" exporting will be effected by this
mechanism.

Implements bp: image-location-selection-strategy

Related-Id: I86f192aeae8e5f21a72f946552f6507654c25a6c
Change-Id: I7bd093a16db3af2b604cad22a6b6971345af82a2
Signed-off-by: Zhi Yan Liu <zhiyanl@cn.ibm.com>
Add unit tests around glance-manage

Adds unit tests around glance-manage

Implements bp adds-tests-around-glance-manage
Change-Id: Ia40030ee00b2555e1ee6f57760d2794a45f25325
Merge "Apply image location selection strategy"