Stringify instance UUID

oslo.versionedobjects merged a patch [1] resulting in the referenced
bug. A second patch [2] was merged that was supposed to fix the issue
If coerce's value arg is a unicode string, then the method will return
unicode [3]. Subsequent checks for isinstance(str) [4] will fail and a
TypeError will be raised trying to handle the uuid as an int in the
else block. This change ensures that the uuid is an instance of str so
that it is handled properly. This problem was fixed in pypowervm 1.1.15
[5] and the minimum version was bumped for master. However, we can't
backport the pypowervm requirements bump to the stable branches so we
have to fix it here.

[1] https://review.openstack.org/#/c/559815/
[2] https://review.openstack.org/#/c/561674/
[3] https://review.openstack.org/#/c/561674/2/oslo_versionedobjects/fields.py@367
[4] https://github.com/powervm/pypowervm/blob/1.1.6/pypowervm/utils/uuid.py#L50-L56
[5] https://github.com/powervm/pypowervm/commit/d55b4c84

Related-Bug: #1766692
Change-Id: Ic3b11b071a055177bbcfb0555e2a391ba419d191
(cherry picked from commit 49330fcf28)

nova_powervm/virt/powervm/vm.py

@@ -754,7 +754,11 @@ def get_pvm_uuid(instance):
     :param instance: nova.objects.instance.Instance
     :return: pvm_uuid.
     """
-    return pvm_uuid.convert_uuid_to_pvm(instance.uuid).upper()
+    # NOTE(esberglu): To work around bug ##1766692, we explicitly use str()
+    # rather than six.text_type here because of this pypowervm check for
+    # isinstance(..., str) at L50 of
+    # https://github.com/powervm/pypowervm/blob/1.1.6/pypowervm/utils/uuid.py
+    return pvm_uuid.convert_uuid_to_pvm(str(instance.uuid)).upper()
 
 
 def _uuid_set_high_bit(pvm_uuid):