This patch provides XmTestManagedDomain and XenManagedDomain classes

This patch provides XmTestManagedDomain and XenManagedDomain classes
similar to the XmTestDomain and XenDomain classes. I have wrapped the
xen-api for VM configuration creation, starting and stopping of VMs and
destruction of the VM configuration in the XenManagedDomain class's
methods. No device-related functions are provided through the class.

The managed domains' UUIDs are tracked and all created VMs are destroyed
upon failure or skipping of the test or by calling
xapi.vm_destroy_all().

I am adding a new grouptest 'xapi' for running xen-api tests.

Only caveat: I am using an empty username and password
(XmTestList/xapi.py) with Xend's authentication deactivated to run these
tests.

Signed-off-by: Stefan Berger <stefanb@us.ibm.com>