MINOR: cfgparse: warn when gid parameter is not a number

Currently, no warning are emitted when the gid is not a number.
Purpose of this warning is to let admins know they their configuration
won't be applied as expected.

(cherry picked from commit 776e518caf10cc76a19278f67800082cfe058723)
(cherry picked from commit baae1475c29f3a3ebd41823a6ea8b215f89a3eb8)
1 file changed