Allow adding or changing the CSS classes of a data table

Sometimes a datatable needs to be displayed slightly differently, for
instance with or without the borders, condensed, zebra, etc. This patch
lets us do that in two ways.

It adds a css_class option to table's Meta, so that we can easily add
more classes to a particular table, and modify its looks with CSS.

It also puts the whole table's CSS class list in a block, so that we
can inherit from the table's template to completely replace its classes,
if we need to.

Change-Id: I64a1f3ba8d80643c545de024f52ec3313bbff8e5
Hiding "Launch as Instance" if volume is not bootable.

If a volume which is not bootable, is used to create an instance
then the instance will go into 'Error' state.
The patch solves this issue by hiding the 'Launch as Instance'
button if the volume is not bootable.

Closes-Bug: #1327310

Change-Id: I3d9e7edf846fafab4e735d562c1ec72ad32fb220
Fix host listing in live migration

The live migration selector needs to offer a list
of hosts, not a list of hypervisors.

Change-Id: I73c1175a5f87b0f91e36083f05467c26feca5d51
Closes-Bug: #1335999
Merge "Allow adding or changing the CSS classes of a data table"
Merge "Hiding "Launch as Instance" if volume is not bootable."
Merge "Fix host listing in live migration"
Merge branch 'master' of https://github.com/openstack/horizon