Fixed version to 2.6.1 and ensure it's working with amazon linux, ubuntu...

...12.04LTS and 14.04LTS, centos6, and debian7 backports and redhat6. 

It supports only 2.6.1 or latest. It creates the admin user with the need mongodb 2.6.1 schema/roles. It also permits to run reconfigure with no errors, as it check for the 252 error if the user already exists.

With redhat, there is another needed fix that is to add to iptables the port, because iptables is enabled by default filtering all. So it's not enough for accessing 27017 from the outside with the security groups of amazon or gce. I've already the code to fix it, but as it's a security issue/decission i want to decide with you if we include it in the manifest or not. If you want i do another PR for it. If not, this is ready to ship. It's working in all the images i know and use normally.

@arnaud-elasticbox
@albertoarias