Refactor mongodb.

These commits break the mongodb class into several classes,
mongodb::install, ::config, and ::service.  It also renames
the mongodb::sources classes to mongodb::repos::$osfamily.

Along side that begin work on cleaning up the API by renaming
many parameters:

version        -> package_ensure
packagename    -> package_name
dbpath         -> dbpath_name
mongo_user     -> user
mongo_group    -> group
logpath        -> logpath_name
config_file    -> config_name
servicename    -> service_name
service_enable -> service_ensure
location       -> repo_location (Also applies to RHEL now)
enable_10gen   -> type (more on this later)

As well as adding:

service_ensure (takes stopped/running)

We now set $type as the first parameter and use this to pull out
all the other defaults, so that we can pick appropriate 10gen vs
non-10gen defaults.  This does mean some distros require duplicate
values for both branches, but this is still cleaner than the if
logic we had before.

I still dislike it but there's no way to get defaults AND allow
a global selector to change which set of defaults is fetched.