Populate image.http_qcow2_image

Since https://review.opendev.org/c/openstack/tempest/+/923357
there is a new config image parameter which requires a qcow2 image.

Populate it (even in case it's not going to be used) using
the same value of DEFAULT_IMAGE, which happens to be qcow2,
trying to balance reducing duplication of the definition
of external resources (cirros images) and the need to have
a separate variable to track this default.

Change-Id: I01187f061b809b4beb29ae5d96e16325052619ed

config_tempest/constants.py

@@ -26,6 +26,9 @@ DEPLOYER_INPUT = os.path.join(os.path.expanduser("~"),
 DEFAULT_IMAGE_DIR = 'etc'
 DEFAULT_IMAGE = ("https://download.cirros-cloud.net/0.6.2/"
                  "cirros-0.6.2-x86_64-disk.img")
+# Should DEFAULT_IMAGE be changed to a format which is not qcow2,
+# then disconnect DEFAULT_IMAGE from DEFAULT_QCOW2_IMAGE
+DEFAULT_QCOW2_IMAGE = DEFAULT_IMAGE
 
 DEFAULT_IMAGES = [("https://download.cirros-cloud.net/0.6.2/"
                   "cirros-0.6.2-x86_64-disk.img"),

config_tempest/services/image.py

@@ -79,6 +79,7 @@ class ImageService(VersionedService):
             # this value can't be set to image.http_image, therefor set the
             # default value
             conf.set('image', 'http_image', C.DEFAULT_IMAGE)
+        conf.set('image', 'http_qcow2_image', C.DEFAULT_QCOW2_IMAGE)
 
     def _is_multistore_enabled(self):
         try: