[WIP] Adapt to upcoming tilelive-bridge

[springmeyer]

Past tilelive-bridge did not validate mapnik XML when the source was created. Therefore you could have a seemingly valid source with a completely invalid XML loaded. This means that the error would only show up at source.getTile. This also meant that a test in studio classic was lurking that was not loading a valid source because the shapefiles were left behind. This pull fixes that problem.

refs mapbox/tilelive-bridge#66

/cc @yhahn @GretaCB @rclark

[springmeyer]

Before this fix, with latest tilelive-bridge, the test would fail with:

TAP version 13
# local: save as tmp => perm
ok 1 null
not ok 2 Error: Shape Plugin: shapefile '/var/folders/jv/bhkldrpj41jbkpzxgc9ggr_r0000gn/T/mapbox-studio/source-saveas-vbozockyxbhuxr/10m-900913-bounding-box.shp' does not exist encountered during parsing of layer 'solid' in Layer
  ---
    operator: error
    expected: |-
      undefined
    actual: |-
      [Error: Shape Plugin: shapefile '/var/folders/jv/bhkldrpj41jbkpzxgc9ggr_r0000gn/T/mapbox-studio/source-saveas-vbozockyxbhuxr/10m-900913-bounding-box.shp' does not exist  encountered during parsing of layer 'solid' in Layer]
    at: done (/Users/dane/projects/mbstudio/lib/source.js:223:25)
    stack: |-
      Error: Shape Plugin: shapefile '/var/folders/jv/bhkldrpj41jbkpzxgc9ggr_r0000gn/T/mapbox-studio/source-saveas-vbozockyxbhuxr/10m-900913-bounding-box.shp' does not exist  encountered during parsing of layer 'solid' in Layer
  ...

[springmeyer]

Travis is green, so merging. Appveyor is failing but unrelated to this pull as far as I can tell:

not ok 294 Error: Active task in progress
  ---
    operator: error
    expected: |-
      undefined
    actual: |-
      [Error: Active task in progress]
    stack: |-
      Error: Active task in progress
          at startUpload (C:\projects\mapbox-studio-classic\lib\source.js:704:41)
          at C:\projects\mapbox-studio-classic\lib\source.js:680:17
          at C:\projects\mapbox-studio-classic\lib\source.js:528:30
          at load (C:\projects\mapbox-studio-classic\lib\source.js:437:16)
          at C:\projects\mapbox-studio-classic\lib\source.js:493:20
          at fs.js:334:14
          at C:\projects\mapbox-studio-classic\node_modules\fstream\node_modules\graceful-fs\graceful-fs.js:42:10
          at FSReqWrap.oncomplete (fs.js:95:15)
  ...
C:\projects\mapbox-studio-classic\test\source.test.js:529
        t.strictEqual(task.id, id, 'sets task.id');
                          ^
TypeError: Cannot read property 'id' of undefined
    at C:\projects\mapbox-studio-classic\test\source.test.js:529:27
    at startUpload (C:\projects\mapbox-studio-classic\lib\source.js:704:32)
    at C:\projects\mapbox-studio-classic\lib\source.js:680:17
    at C:\projects\mapbox-studio-classic\lib\source.js:528:30
    at load (C:\projects\mapbox-studio-classic\lib\source.js:437:16)
    at C:\projects\mapbox-studio-classic\lib\source.js:493:20
    at fs.js:334:14
    at C:\projects\mapbox-studio-classic\node_modules\fstream\node_modules\graceful-fs\graceful-fs.js:42:10
    at FSReqWrap.oncomplete (fs.js:95:15)
npm ERR! Test failed.  See above for more details.
error during "npm test"