software/slapos-sr-testing: install python-cliff explicitly

software/slapos-sr-testing/software.cfg

@@ -2,6 +2,7 @@
 
 extends =
   ../../component/bcrypt/buildout.cfg
+  ../../component/python-cliff/buildout.cfg
   ../../component/curl/buildout.cfg
   ../../component/openssl/buildout.cfg
   ../../component/git/buildout.cfg
@@ -185,6 +186,7 @@ setup = ${slapos.core-repository:location}
 [python-interpreter]
 eggs += ${:extra-eggs}
 extra-eggs =
+  ${python-cliff:egg}
   ${lxml-python:egg}
   ${slapos.core-setup:egg}
   ${pillow-python:egg}