Test for python-pip as well as pip

On Red Hat, CentOS and Fedora systems, the pip binary will be called python-pip
instead of pip. This commit makes the pip module also check for python-pip.

The reason we check for python-pip *first*, is to have ansible fail on not
finding 'pip' and reporting *that*. This is consistent with current behaviour
and will not confuse users of Debian et al., where the 'python-pip' binary
never exists.

Tested on Fedora 18 and Ubuntu 12.04.

pip

@@ -135,6 +135,8 @@ def main():
         out += out_venv
         err += err_venv
 
+    pip = module.get_bin_path('python-pip', False, ['%s/bin' % env])
+    if not pip:
         pip = module.get_bin_path('pip', True, ['%s/bin' % env])
 
     state = module.params['state']