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
Merge "Makes 'expires_at' not appear if not set on task"
Merge "Remove vim header"