Remove 'openstack/common/context.py'
Remove 'openstack/common/context.py'

context.py is not used anywhere in Glance. Consequently, we can get
rid of it.
Also, context.py is the only file left using uuidutils.

Change-Id: I657e20ac39fbace60f230652912a4bf792836206
Closes-Bug: #1253497

redhat-openstack/glance,tanglei528/glance,openstack/glance,takeshineshiro/glance,stevelle/glance,wkoathp/glance,klmitch/glance,JioCloud/glance,akash1808/glance,saeki-masaki/glance,scripnichenko/glance,darren-wang/gl,akash1808/glance,redhat-openstack/glance,kfwang/Glance-OVA-OVF,sigmavirus24/glance,openstack/glance,jumpstarter-io/glance,rajalokan/glance,dims/glance,jumpstarter-io/glance,JioCloud/glance,klmitch/glance,dims/glance,ozamiatin/glance,kfwang/Glance-OVA-OVF,paramite/glance,vuntz/glance,wkoathp/glance,paramite/glance,sigmavirus24/glance,tanglei528/glance,openstack/glance,takeshineshiro/glance,scripnichenko/glance,stevelle/glance,ozamiatin/glance,saeki-masaki/glance,darren-wang/gl,rajalokan/glance,vuntz/glance