'Validate self.vm_size against the list of virtual machine sizes available for the account and location.
:return: boolean'

def vm_size_is_valid(self):

    try:
        sizes = self.compute_client.virtual_machine_sizes.list(self.location)
    except Exception as exc:
        self.fail('Error    retrieving    available    machine    sizes    -    {0}'.format(str(exc)))
    for size in sizes:
        if (size.name == self.vm_size):
            return True
    return False
