common/rc: fix group detection regex to strictly match required name

common/rc: fix group detection regex to strictly match required name

_require_group greps for the required group string in /etc/group but
this can partially match other groups or group member names and falsely
return success where it should fail.

Make the regex more specific so that it can unambigiously match only the
exact group name rather than any other group that happens to match as a
substring or any matching username from the group member list field.

Signed-off-by: Anthony Iliopoulos <ailiop@suse.com>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>