Add menu regions to integration tests

Adding menu regions.

* DropDownMenuRegion - base drop down menu region class
* UserDropDownMenuRegion - menu located in the top right corner

Partially implements blueprint: selenium-integration-testing

Change-Id: I611b46153d0f38a588ee931c954f771306802f14
Fix popup error when volume service disabled

In an enviroment, where cinder is disabled, I'm getting error popups
when trying to 'launch instance':
Error: Unable to retrieve list of volumes.
Error: Unable to retrieve list of volume snapshots.
So we need to make sure whether the volume service exists when
calling the cinder api in the launch instance workflow.

Closes-bug: #1394900

Change-Id: I6f745f7f95272eb87b6d867d76d7726c7eb5bb24
Add 'Start/Stop Instance' to Instances table actions

Some users have been reporting that they would like the ability to
start multiple instances at once, for instance after an upgrade it's
common for the instances to be shut off and need to be manually
restarted.

This patch adds 'Start Instances', 'Stop Instance' and moves
'Soft Reboot Instances' to the Instances table actions menu which is
a recently implemented feature.

Change-Id: I3c3b29a92fe61e6330b60c3d2228d899c409c23a
Closes-bug: #1354395
Change "Modify Users" to "Manage Members"

Change "Modify Users" to "Manage Members" in the Project, Group and
Domain Panels in-row Actions. This allows us to be consistent with the
tab headings in both panels.

Change-Id: I7f99624efe623d3cb7fe5861c9cd8ceab8ca3661
Closes-bug: #1398224
Merge "Add menu regions to integration tests"
Merge "Add 'Start/Stop Instance' to Instances table actions"
Merge "Fix popup error when volume service disabled"
Merge branch 'master' of https://github.com/openstack/horizon