No mbpi add custom

This change does the following:

 - it renames the android-provision plugin to ubuntu-provision
 - it renames the helper android-apndb.* files to ubuntu-apndb.*
 - it removes support for the mbpi database
 - it adds support for customization via /custom/etc/apns-conf.xml
   ( https://bugs.launchpad.net/ubuntu/+source/ofono/+bug/1315509 )

The custom file is read first, and if any mvno matches are found, provisioning ends ( ie. /system/etc/apns-conf.xml is not queried ).  If no mvno matches are found, then the /system file is next queried.  If any mvno matches are found, the list is trimmed to just those matches.  Finally the two lists are merged.  If an apn is found in /custom which matches the type and 'apn' attribute of a /system apn, then the custom one is used.

This has been tested on mako, running image #u132.
The original logic was that if *any* mvno apns were found, then any non-mvno apns are tossed out.  If you match on a mvno in custom, then why would you want to bother with querying against the base db?

I guess one reason would be that it would be possible to correct a mistake in a mvno apn ( say for MMS-only ), and still pick up the internet apn from the base db.

Let me give this some thought.  It was a last minute addition, as I had no clear guidelines on how to implement /custom.

That said, are you comfortable with the logic in merge_apn_lists()?
keep a non-mvno apn in the mix?  Also, if you add a new mvno apn ( or a corrected mvno apn ) to custom, it would seem a reasonable restriction that you need to cover Internet & MMS in the custom file