Make port definition optional

Based on the use of the mongod process it should listen on a different
port[1]. configsvr should be listening on 27019 and shardsvr on 27018.
Currently, since the port is speficied in both init.pp and server.pp
even though the server is start on the mode mentioned above it will
listen on 27017, which is wrong. It is backward compatible since by
default if no port is specified it will listen on 27017

[1] http://docs.mongodb.org/manual/reference/default-mongodb-port/
[DO NOT MERGE] Ensure rs.conf() is run on the proper mongod process

Currently, rs.conf() can only be run on 127.0.0.1:27017.
When running a node in shardsvr mode, the mongod process
listens on port 27018, hence the rs.conf() check fails.

DO NOT MERGE IT YET UNTIL WE FIND A PUPPET WAY TO DO THAT.
SO FAR ITS JUST A DIRTY HACK TO GET ME GOING WITH MY END GOAL.
Add support for mongos configuration
Implement Sharding Support

This patch aims to support MongoDB sharding feature.

* Enable Sharding in MongoDB configuration file if enabled (disabled by
  default).
* Add a Type and a Provider to manage a MongoDB Shard resource.
* Add tests/sharding.pp to show an example of usage.
* Update the documentation about MongoDB Sharding usage.
* Unit tests for the new Type and the new Provider.

Conflicts:
	manifests/server.pp