koji.sh: support testing of upload to the cloud

Extend the `koji.sh` test case to allow also testing the upload to
cloud, in addition to the testing that it supports currently (building
of multiple images in one Koji compose request).

The script now reuses some common functions used by the `api.sh` test
case. Once the Koji compose succeeds, the script verifies that the image
is present in the appropriate cloud environment using a CLI tool. No
additional testing of the image is done, it is not booted.

test/cases/api/common/aws.sh

@@ -31,3 +31,10 @@ function installClient() {
   fi
   $GOVC_CMD version
 }
+
+# Log into AWS
+# AWS does not need explicit login, but define this function for the sake of
+# consistency to allow calling scripts to not care about cloud differences
+function cloud_login() {
+  true
+}