[CB-2213] Added a new test for readAsDataURL.

This test uses a FileEntry created using a native URI.
[CB-2213] Added a new test for getMetadata.

Also consolidated NATIVE_URI tests.
[CB-2213] Added three new tests to Camera.

The tests ensure that FileEntry.remove, FileEntry.setMetadata, and FileReader.readAsText return errors when used with a native URI.