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
Remove vim header

No need to set tabstop tons of times, this can be set in your vimrc
file instead.

More disucssion:
http://openstack.10931.n7.nabble.com/Remove-vim-modelines-td21780.html

Change-Id: I3b830a5bb831a63c188109e6fad66ba48884fff3
Partial-Bug: #1229324
Makes 'expires_at' not appear if not set on task

Fixes bug: 1267148

'expires_at' on a task must be set only after the executor succeeds or
fails on a task. Before the task has finished, there shouldn't be any
'expires_at' set on the task. This change fixes the ResponseSerializer
to not show 'expires_at' if it is not set.

Change-Id: I9880cc03b9d6f0dd98388fcf0d1bdc9c34dd6c0e
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 "Makes 'expires_at' not appear if not set on task"
Merge "Remove vim header"
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"