action #3078 - adapt check_command to the new dashboard route

Now `osc staging check A` generate a request to:
   GET https://api.opensuse.org/distributions/openSUSE:13.2/staging_projects/A.json

and `osc staging -p 13.2 check A` to:
   GET https://api.opensuse.org/distributions/openSUSE:Factory/staging_projects/A.json