Daemon user created.

The mongod daemon runs as the user mongodb, who needs the proper
permissions over the dbpath and logpath.
Restart instead of reload.

The init script does not seem to support reloading, when called the
process is terminated and restarted - use restart instead.

Also, moved away from using handlers for restarting after configuration
changes because handlers are not properly flushed between roles in a
play. So if one role in a play starts mongod and another role in the
play relies on it, problems arise as the handlers are flushed between
plays and there is no convenient way to call meta: flush_handlers
between roles.