Updates to run multiple instances of memcached.

Hi.  I have the same needs as discussed in https://github.com/saz/puppet-memcached/issues/18 so here's a PR to cover it.

I run rhel/centos servers so that is the only platform that I functionally tested.  I took a look at the startup scripts in the Debian package and it looks like this implementation should work, but its worth someone testing.  The difference as far as I can tell is that Debian will only have 1 service definition which manages all of the memcached instances whereas the other OS's have a service def for each instance.

For this implementation I removed the ability to specify the logfile, pidfile, and user.  It was necessary for the changes here and I don't feel like this will cause people major issues.  If you disagree perhaps we can come up with a middle ground solution.

Hello !

The default Debian 7 Memcached init script already handle multiple instances : 

```bash
#! /bin/bash
### BEGIN INIT INFO
# Provides:            memcached
# Required-Start:      $remote_fs $syslog
# Required-Stop:       $remote_fs $syslog
# Should-Start:                $local_fs
# Should-Stop:         $local_fs
# Default-Start:       2 3 4 5
# Default-Stop:                0 1 6
# Short-Description:   Start memcached daemon
# Description:         Start up memcached, a high-performance memory caching daemon
### END INIT INFO

# Usage:
# cp /etc/memcached.conf /etc/memcached_server1.conf
# cp /etc/memcached.conf /etc/memcached_server2.conf
# start all instances:
# /etc/init.d/memcached start
# start one instance:
# /etc/init.d/memcached start server1
# stop all instances:
# /etc/init.d/memcached stop
# stop one instance:
# /etc/init.d/memcached stop server1
# There is no "status" command.

PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin
DAEMON=/usr/bin/memcached
DAEMONNAME=memcached
DAEMONBOOTSTRAP=/usr/share/memcached/scripts/start-memcached
DESC=memcached

test -x $DAEMON || exit 0
test -x $DAEMONBOOTSTRAP || exit 0

set -e

. /lib/lsb/init-functions

# Edit /etc/default/memcached to change this.
ENABLE_MEMCACHED=no
test -r /etc/default/memcached && . /etc/default/memcached


FILES=(/etc/memcached_*.conf)
# check for alternative config schema
if [ -r "${FILES[0]}" ]; then
  CONFIGS=()
  for FILE in "${FILES[@]}";
  do
    # remove prefix
    NAME=${FILE#/etc/}
    # remove suffix
    NAME=${NAME%.conf}

    # check optional second param
    if [ $# -ne 2 ];
    then
      # add to config array
      CONFIGS+=($NAME)
    elif [ "memcached_$2" == "$NAME" ];
    then
      # use only one memcached
      CONFIGS=($NAME)
      break;
    fi;
  done;

  if [ ${#CONFIGS[@]} == 0 ];
  then
    echo "Config not exist for: $2" >&2
    exit 1
  fi;
else
  CONFIGS=(memcached)
fi;

CONFIG_NUM=${#CONFIGS[@]}
for ((i=0; i < $CONFIG_NUM; i++)); do
  NAME=${CONFIGS[${i}]}
  PIDFILE="/var/run/${NAME}.pid"

case "$1" in
  start)
       echo -n "Starting $DESC: "
       if [ $ENABLE_MEMCACHED = yes ]; then
            start-stop-daemon --start --quiet --exec "$DAEMONBOOTSTRAP" -- /etc/${NAME}.conf $PIDFILE
            echo "$NAME."
       else
            echo "$NAME disabled in /etc/default/memcached."
       fi
       ;;
  stop)
       echo -n "Stopping $DESC: "
       start-stop-daemon --stop --quiet --oknodo --retry 5 --pidfile $PIDFILE --exec $DAEMON
       echo "$NAME."
       rm -f $PIDFILE
       ;;

  restart|force-reload)
       #
       #       If the "reload" option is implemented, move the "force-reload"
       #       option to the "reload" entry above. If not, "force-reload" is
       #       just the same as "restart".
       #
       echo -n "Restarting $DESC: "
       start-stop-daemon --stop --quiet --oknodo --retry 5 --pidfile $PIDFILE
       rm -f $PIDFILE
       if [ $ENABLE_MEMCACHED = yes ]; then
       		start-stop-daemon --start --quiet --exec "$DAEMONBOOTSTRAP" -- /etc/${NAME}.conf $PIDFILE
       		echo "$NAME."
       else
            echo "$NAME disabled in /etc/default/memcached."
       fi
       ;;
  status)
       status_of_proc -p $PIDFILE $DAEMON $NAME  && exit 0 || exit $?
       ;;
  *)
	N=/etc/init.d/$NAME
	echo "Usage: $N {start|stop|restart|force-reload|status}" >&2
	exit 1
	;;
esac
done;

exit 0
```