model: Handle libvirt connection failures

V1->V2:
 - Use startswith for some string comparisons

If the libvirt daemon goes down, any cached libvirt objects (including
connections) become invalid.  To improve resiliency, we should handle
two cases:

1) Libvirtd is restarted:  Fail the current operation and allow
subsequent operations to re-establish a connection to the new libvirtd
instance.

2) Libvirtd is stopped or crashed:  Retry the connection a couple of
times and then shut down since we cannot operate without a running
libvirt daemon.

We accomplish the above two use cases by wrapping all functions in the
libvirt module with code that traps connection errors and responds
appropriately.

Also, make the Guests tab in the UI handle intermittent failures by
retrying even after failure.

Signed-off-by: Adam Litke <agl@linux.vnet.ibm.com>
Apply Kimchi style to login screen

The login screen was not in the Kimchi pattern.
When comparing it with other pop-up screens the background color and borders
style were different.
Fix it to use the same style pattern in all application.

Signed-off-by: Aline Manera <alinefm@br.ibm.com>