Add rules_pkg to the list of test repositories set up for shell integ…

…ration tests. Commit b7a79ff depends on this. This is a partial cherrypick of e9929af.

src/test/shell/testenv.sh.tmpl

@@ -330,6 +330,7 @@ EOF
         "rules_license"
         "rules_proto"
         "rules_python"
+        "rules_pkg"
     )
     for repo in "${repos[@]}"; do
       reponame="${repo%"_for_testing"}"