* [tests] Implement filtering based on test name to make it possible to run a subset of tests manually.
* [xharness] Add support for passing environment variables to test apps.
* [xharness] Split the mscorlib/System test run for watchOS into multiple executions.
When running on a watch, the complete set of mscorlib and System tests use too
much memory, so they end up crashing the app.
So instead don't run all the tests in the same test run, but
instead split them up.
This splits the System tests in 5 different sets, based on the first
character of the test class name.
The mscorlib tests are split in 26 different sets, one for each
character (A-Z).
Rolf Bjarne Kvinge