Update Tox JJB Command

This allows using the command to only test one project's changes. For
example:

  tox -e jjb -- jjb/releng

Will only test jobs under 'jjb/releng'. If jobs have dependencies, of
multiple project jobs need to be tested, they can be included using the
jjb ':' syntax, as anything after '--' is passed directly to jjb:

  tox -e jjb -- jjb/doctor:jjb/functest

Change-Id: I4b71803a1d6ed4f62d50cdca87183a68b20fae5a
Signed-off-by: Trevor Bramwell <[email protected]>

docs/infra/jenkins/jjb-usage.rst

@@ -31,6 +31,12 @@ Test with tox::
 
     tox -v -ejjb
 
+.. note:: You can also test the jobs under a single jjb directory by
+    specifying the directory. For example to test only the releng jobs, you
+    could run:
+
+     tox -v -e jjb -- jjb/releng
+
 Submit the change to gerrit::
 
     git review -v

tox.ini

@@ -17,4 +17,4 @@ setenv=
 deps =
   jenkins-job-builder==1.6.1
 commands=
-  jenkins-jobs test -o job_output -r jjb/
+  jenkins-jobs test -o job_output -r jjb/global:{posargs:"jjb/"}