CB-8125: Reorganize and clean up test suite.

Audited all calls to done() to ensure correct async execution. Removed some redundant code. Removed depencency on mobile-spec: tests now run even if started independently. Tested without plugin-test-framework and with it, on Windows, iOS, and Android.

Made deleteFile and writeFile raise real errors when they encounter real problems; otherwise, made their logging sound less threatening. Fixed spec.17, using localFilePath instead of fileName.

Fixed issue with pending() throwing errors when being called in an async 'unsupported' callback by calling it in afterEach. Also made log messages slightly more informative.

This closes #55
CB-8125: Fix spec tests 28 and 29

These tests had long been failing (silently). The refactor for CB-8125
surfaced those failures, and so this fixes them.