Refactors BitmapRetrieverTest.cacheImage (inc rename)
Refactors IM.cacheImage - WIP (fails)
Removes redundant (and failing test) from ImageManager.

- Removes ImageManagerTest.testCacheImage
- The behaviour it tests is covered in ImageManagerInstrumentationTest.testCacheImage
Removes unused fields
Changes test image (want to trigger build)
Adds LruBitmapCache to LoaderSettings used in testCacheImage
provide image to avoid loading via network
make test intention more clear
Implements NetworkManager instead of FileManager to fix error (WIP).

- The error caused on instrumentation test devices was due to lack of network connection
- we should emulate the networkmanager, not the filemanager
- :x: the tests don't complete - it's stuck on

    > Building > :demo:connectedInstrumentTest (no errors)
Adds nullcheck to outputstream
Sets width and height to non-zero values.

- Using width and height as 0 caused the looping for some uninvestigated (as of yet) reason.
Tidies utility method by reusing code (FileUtil)

- The test was failing on CI because one of the devices had no available space
- ImageLoader failed gracefully (didn't cache), but the test failed because the test is to check it can cache
Splits BitmapRetrieverTest into two tests
Makes superfluous changes to test PRB
Makes test names consistent
Merge pull request #145 from novoda/fix_testCacheImage_test_fails

Fix test cache image test fails