systemd: add PATH for finding systemctl

The 1.3.0 release adds a call to systemctl fails for it's in /usr/bin.

[root@localhost nfs-utils]# start-statd
/usr/sbin/start-statd: line 9: systemctl: command not found
Statd service already running!

Reported-by: Allan Duncan <amd1234@fastmail.com.au>
Signed-off-by: Kinglong Mee <kinglongmee@gmail.com>
Signed-off-by: Steve Dickson <steved@redhat.com>