Check MongoDB server is working.

This patch makes MongoDBLauncher throw ServerNotRespondingException when
the server does not respond.
LauncherSupervisor makes MongoDBLauncher restart.

MongoDBLaucher uses Status command for health checking.
Add ProcessLauncher.

The launcher who inherits ProcessLauncher have to early initialize
pidFileName, initialDelay and tickInterval. These are used by
constructor.
ProcessLauncher launches process when ProcessLauncher starts if pid file
is not exists. And kills process when restarts.

The next patch will make MongoDBLauncher and ZooKeeperLauncher inherit it.
Make MongoDBLauncher inherit ProcessLauncher.
Make ZooKeeperLauncher inherit ProcessLauncher.