conf/redhat: Prevent killproc from removing /usr/sbin/puppetmasterd

Mattias Saou ran into a serious bug cause by 9dff71 (Use -p option to
killproc). The puppetmaster init script lacked a pidfile variable,
which ended up with /usr/sbin/puppetmasterd being removed.

Signed-off-by: Todd Zullinger <tmz@pobox.com>