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

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.
I know this was here from before, but anyway: I have been testing with a DB coming from one Android phone and it had a couple of APNs that were wrong, because of missing mcc/mcn or apn field. That set the error variable, and the consequence was that the whole DB was thrown away and no context was configured. I think we should just return here and process the next entry, that would be harmless and we could deal with not 100% right databases. Take into account that DBs are big, are edited by the OEM, and more often than not one or another entry can be wrong. We could print a call with ofono_error() instead to help OEMs to debug.