sysvinit: allow users in shutdown group to perform halt/reboot

sysvinit: allow users in shutdown group to perform halt/reboot

For this to happen:
 * 'shutdown' group has been created;
 * changed ownership group for /sbin/halt and /sbin/shutdown to 'shutdown';
 * deny execution rights to other users except 'root' and those belonging
   to 'shutdown' group;
 * set setuid bit to both apps;

So, basically, in order for a normal user to be able to shutdown/reboot
the machine, it must be a member of 'shutdown' group.

Other changes:
 * fixed identation for 2 lines that used spaces instead of tabs;

[YOCTO #4345]

(From OE-Core rev: b32d06fbe797cd39cc19f62bda8a698effe7c0ea)

Signed-off-by: Laurentiu Palcu <laurentiu.palcu@intel.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>