bin/hadoop should allow callers to set jsvc pidfile even when not-detached

it would be nice if the jsvc pid file were properly namespaced in /var/run to avoid collisions with other jsvc instances

jsvc uses /var/run/jsvc.pid for the datanode pid file. If that's configurable, it should be configured: /var/run/jsvc.pid is sorely not namespaced.

if [ "$_HADOOP_DAEMON_DETACHED" = "true" ]; then
_JSVC_FLAGS="-pidfile $_HADOOP_DAEMON_PIDFILE
-errfile &1
-outfile $_HADOOP_DAEMON_OUT"
else

1. Even though we are trying to run a non-detached datanode,
2. jsvc will not write to stdout/stderr, so we have to pipe
3. it and tail the logfile.
   log_path=/tmp/jsvc_${COMMAND}.$$
   _JSVC_FLAGS="-nodetach
   -errfile &1
   -outfile $log_path"
   echo Non-detached jsvc output piping to: $log_path
   touch $log_path
   tail -f $log_path &
   fi

And the relevant argument is '-pidfile' (http://linux.die.net/man/1/jsvc).