fix bug 928051 - get b2g into reports_clean

Putting this up for discussion - it does the bare minimum to get b2g reports into ```product_versions``` and also ```reports_clean```. I have only been able to test this locally using fakedata, you must modify the rewrite JSON in ```update_channel_map``` like so (this is a ```copy from update_channel_map with csv```):

```
nightly,{3c2e2abc-06d4-11e1-ac3b-374f68613e61},B2G_OS_Version,"{""Android_Manufacturer"": ""ZTE"",
           ""Android_Model"": ""roamer2"",
           ""Android_Version"": ""15(REL)"",
           ""B2G_OS_Version"": ""1.0.1.0-prerelease"",
           ""BuildID"":
                [""20140216000020"", ""20130621152332"",
                 ""20130531232151"", ""20130617105829"",
                 ""20130724040538""],
            ""ProductName"": ""B2G"",
            ""ReleaseChannel"": ""nightly"",
            ""Version"": ""18.0"",
            ""rewrite_update_channel_to"": ""release-zte"",
            ""rewrite_build_type_to"": ""release""}"
```

Note that the ```BuildID``` array has at least one entry that matches my local fakedata (which changes depending on the day it is generated).

When I have the above entry and backfill, I see B2G data in ```reports_clean``` (and also ```product_versions``` which is currently a prereq).

@selenamarie - we discussed also having an ```update_channel``` in ```product_versions```, which would be set to ```release-zte``` in this case. What else is this patch missing ? :) I *think* if we took it as-is, we'd at least be able to start getting crashes for shipped phones into ```reports_clean``` and all the dependent reports like topcrashers, assuming that ```update_channel_map``` is filled out correctly.