Fix a warning when running `tox -e api-ref`

When executing `tox -e api-ref`, the following warning appears.

    WARNING:test command found but not installed in testenv
      cmd: /bin/rm
      env: /Users/tl3438/oss/ceilometer/.tox/api-ref
    Maybe you forgot to specify a dependency? See also ...

This patch set adds the whitelist_externals to api-ref.

Change-Id: Ic663d229990c028888f0ecd7f7b85561ad618bf4

1 files changed, 1 insertions, 0 deletions

diff --git a/tox.ini b/tox.ini
index fd328a28..03143eb5 100644
--- a/tox.ini
+++ b/tox.ini
@@ -140,6 +140,7 @@ import_exceptions =
 local-check-factory = ceilometer.hacking.checks.factory
 
 [testenv:api-ref]
+whitelist_externals = rm
 commands =
   rm -rf api-ref/build
   sphinx-build -W -b html -d api-ref/build/doctrees api-ref/source api-ref/build/html