ci: Install kola tests

This builds on
https://github.com/coreos/coreos-assembler/pull/1441
to install our tests rather than running them from the source
directory.  This model will more cleanly allow us to ship
our tests along with a test container or elsewhere, separate
from the source directory.

Also prep for https://github.com/ostreedev/ostree/pull/2048

.cci.jenkinsfile

@@ -76,6 +76,9 @@ parallel fcos: {
         rmdir insttree
         coreos-assembler fetch
         coreos-assembler build
+        # Install the tests, then be sure they're not run again
+        make -C tests/kola install
+        rm tests/kola -rf
       """)
     }
     fcosKola(cosaDir: "${env.WORKSPACE}")