Unit test fixes

Unit test fixes

First, the AddonsListFetcherTest#testLoadSample_1 was failing on the
Mac, because the source code contained non-ASCII unicode characters,
and the encoding differs between Windows, Linux and Mac -- and on the
Mac the characters were garbage (not the intended Japanese
characters). Fixed by using unicode escape sequences to define the
expected output instead.

Second, rename the AbstractLayoutTest to LayoutTestBase; the test
runner (for plugins, not unit tests) was assuming this was a test case
(even though it's an abstract class!) so it was emitting a warning
about the class containing no test cases. This is simply a base class
for all the individual layout tests defining a bunch of useful
inherited shared behavior, so rename to avoid the warning.

Change-Id: I6e29316c5644db35051218aef8b99ac41ab0cda4