Update for stable/queens

Update defaultbranch in .gitreview file.

Update snapcraft to build for queens.

Change-Id: I5bb0251b0177b7c8dd1395ae696fa5ad9e428569

.gitreview

@@ -2,4 +2,4 @@
 host=review.opendev.org
 port=29418
 project=x/snap-openstackclients.git
-defaultbranch=stable/stein
+defaultbranch=stable/queens

snapcraft.yaml

@@ -1,5 +1,5 @@
 name: openstackclients
-version: stein
+version: queens
 summary: OpenStack Client tools
 description: |
   OpenStackClient (aka OSC) is a command-line client for OpenStack
@@ -187,7 +187,7 @@ parts:
       - setuptools_scm
       - toml
     constraints:
-      - https://raw.githubusercontent.com/openstack/requirements/stable/stein/upper-constraints.txt
+      - https://raw.githubusercontent.com/openstack/requirements/stable/queens/upper-constraints.txt
     build-packages:
       - libffi-dev
       - libssl-dev