tests: fix DebOps tests for new image tag names.

.travis/debops_tests.sh

@@ -4,6 +4,7 @@
 TMPDIR="/tmp/debops-$$"
 TRAVIS_BUILD_DIR="${TRAVIS_BUILD_DIR:-`pwd`}"
 TARGET_COUNT="${TARGET_COUNT:-4}"
+MITOGEN_TEST_DISTRO=debian  # Naturally DebOps only supports Debian.
 
 export PYTHONPATH="${PYTHONPATH}:${TRAVIS_BUILD_DIR}"
 
@@ -56,7 +57,7 @@ do
         --detach \
         --publish 0.0.0.0:$port:22/tcp \
         --name=target$i \
-        d2mw/mitogen-test
+        d2mw/mitogen-${MITOGEN_TEST_DISTRO}-test
 
     echo \
         target$i \