Better notification on virtual machine spawn failures

When nova-scheduler fails to spawn virtual machine, e.g. because it
cannot find good compute node to run it, nova silently puts this
new instance into ERROR state, but does not return error to API caller.

To make user aware of such failures we detect them by looking at
created server's state and hostId, and show error messages if
appropriate.

Change-Id: Id4b295fbe0c3e3fdc1aff3e097e656519924132a
Add VM status description to VM details page

If no suitable host was found to launch the VM, make user
aware of such failure by looking at server's status and hostId.

Change-Id: I07bcee3863e498df49b6c243001ea340bc7d8e79