Silence tox warning

tox -e genconfig and tox -e pylint both will generate a warning like:
WARNING:test command found but not installed in testenv
  cmd: /bin/bash
  env: /home/aj/vcs/OpenStack/openstack/manila/.tox/genconfig
Maybe forgot to specify a dependency?

Whitelist bash to remove the warning.

Change-Id: Ibab38ce2308760c7089d5d3e298bfc642367e7b4

tox.ini

@@ -20,6 +20,7 @@ commands =
   flake8 --filename=manila* bin
 
 [testenv:genconfig]
+whitelist_externals = bash
 commands =
   bash tools/config/generate_sample.sh -o etc/manila
 
@@ -37,6 +38,7 @@ commands =
 [testenv:pylint]
 deps = -r{toxinidir}/requirements.txt
        pylint==0.26.0
+whitelist_externals = bash
 commands = bash tools/lintstack.sh
 
 [flake8]