Added service_enable parameter.

Before this change, the mongodb service was started automatically.
This update adds a parameter that allows the service to be
configured and installed without automatically starting it.

Closes #21
Merge pull request #57 from hogepodge/service_enable

Added service_enable parameter.
Added default for all four installation types

Each configuration of MongoDB, across repository and OS, has a
slightly different default configuration. Before this change,
the default configurations were not captured within the module.
After this update, all of the configurations attempt to match
the defaults provided by the source packages.
Fixed whitespace.
Merge pull request #58 from hogepodge/update_defaults

Added default for all four installation types