Bump hacking to 0.8 and get python 3.x compatibility

Bump hacking dependency to 0.8 to get python 3.x compatibility
Fixes done in order to avoid errors after enabling hacking 0.8

Change-Id: Ic878fe2e1bd3f65f7f95a9b5c7a192dac81b749d
Closes-Bug: #1257282
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
add log for _get_images method

The _get_images method in glance/registry/api/v1/images.py doesn't
give logs when catch exceptions. Two logs for two different
exceptions will be very useful for debug.

Change-Id: I5725da0dafdb9909de1c31734b3c1c225483ca66
Closes-Bug:#1263871
Merge "Remove 'openstack/common/context.py'"
Merge "Bump hacking to 0.8 and get python 3.x compatibility"
Merge "add log for _get_images method"