Fix more OS-DCF:diskConfig XML handling

Add handling in the deserialisation code to handle the
OS-DCF:diskConfig attribute in the rebuild and resize actions so
the diskConfig extension can handle it properly. Formerly only
the older auto_disk_config attribute was managed (and incorrectly so).

Fixes bug 1153133

Change-Id: I68479d258cf23083274dd21b1f9eabab2feeb093
Fix RequestContext crashes w/ no service catalog

Code introduced in a prev review assumed service_catalog will be
at least an empty list and will never be None.  But missed one code
path where the service_catalog could potentially be set to None. So
this change switches back the default value of service_catalog in
the arguments to None and makes sure we tolerate anyone else
passing in a None or Empty list as service_catalog

Fix for LP# 1156730

Change-Id: I480b761d57c4699ea7ef72114160cdbeb281e454
Fixes PowerVM spawn failed as missing attr supported_instances

During test in a cross-hypervisor environment (KVM+PowerVM), user will run
into an issue during deploying an instance for Power host by PowerVM driver,
though the property "hypervisor_type" for the PowerVM image have been
configured. Since the _update_host_stats of PowerVM driver missing the
attribute "supported_instances".

Fixes bug: 1155498

Change-Id: I81259d153a7b5ae35747e57c53b14e0075d28d78
Require netaddr>=0.7.6 to avoid UnboundLocalError

This issue is discussed at https://github.com/drkjam/netaddr/issues/2.
The bug in netaddr was fixed in release 0.7.6 on 13th Sep 2011.

Change-Id: Iea75a30963a09f9b0dd94138460bf041ab98fc66
Fixes: bug #1157058
Merge "Fix more OS-DCF:diskConfig XML handling"
Merge "Require netaddr>=0.7.6 to avoid UnboundLocalError"
Merge "Fix RequestContext crashes w/ no service catalog"
Merge "Fixes PowerVM spawn failed as missing attr supported_instances"