Modify and test GDAL_DATA behavior

[springmeyer]

• If GDAL_DATA environment option is set, respect it
• If the local data_path does not exist, throw (to prevent odd errors if mistakenly deleted)
• Add tests for respecting GDAL_DATA environment options
• Add tests for behavior of using local data by default

/cc @BergWerkGIS

[springmeyer]

Motivation for this:

• node-mapnik also bundles GDAL data files. For apps like Mapbox Studio Classic that depend on both node-mapnik and node-gdal and get redistributed as a package, to save space it makes sense to only keep one of the gdal data directories.
• Currently Mapbox studio build scripts drop the node-gdal/deps directory to avoid keeping the c/c++ source files for dependencies (https://github.com/mapbox/mapbox-studio-classic/blob/mb-pages/scripts/build-atom.sh#L89). This was unintentionally also dropping the data. Ideally to avoid this potential in the future the data directory could be moved into ./lib/ - let's discuss at Bundle gdal data inside ./lib? #135

[springmeyer]

@BergWerkGIS - could I summon your help on finishing this work? Basically all tests are passing on unix but on Windows, with some versions of node, the tests are hitting a windows PATH quoting issue:

ok 14 gdal "config" property GDAL_DATA behavior should set GDAL_DATA config option to locally bundled path
not ok 15 gdal "config" property GDAL_DATA behavior should respect GDAL_DATA environment over locally bundled path
  Error: Command failed: 'C:\Program\' is not recognized as an internal or external command,  
  operable program or batch file.  

      at ChildProcess.exithandler (child_process.js:658:15)
      at ChildProcess.emit (events.js:98:17)
      at maybeClose (child_process.js:766:16)
      at Socket.<anonymous> (child_process.js:979:11)
      at Socket.emit (events.js:95:17)
      at Pipe.close (net.js:466:12)

Curiously only with the nodejs provided binaries (https://ci.appveyor.com/project/brianreavis/node-gdal/build/593) and not the mapbox compiled ones. Anyway, can you try replicating locally and see if you can find the right quoting incantation?

[wilhelmberg]

After a quick glance at the test, double quotes around execPath should solve this.
Something like execPath = '"'+ execPath + '"'
Will take a deeper look tomorrow.

[wilhelmberg]

@springmeyer AppVeyor looking ✅
https://ci.appveyor.com/project/brianreavis/node-gdal/build/599

[springmeyer]

Thank you @BergWerkGIS!

@brandonreavis @brandonreavis - any questions or concerns on this? Otherwise I'll merge tomorrow.

[brianreavis]

@springmeyer @BergWerkGIS Looks perfect. Go for it!