cc_test wrapper with a starlark transition

the test_arg_cc_test macro in defs.bzl defines a wrapper for basically a cc_test that has been transitioned. This allows, e.g., the test itself to select attribute values based on the value of that transition. There is some light magic in the transition_rule implementation that allows dependents of the test_arg_cc_test macros to treat the targets it creates the exact same as a regular cc_test.

To run this example:

$ bazel test :all --test_output=all

==================== Test output for //:my-test:

################################################################################
MYTEST ARGV[0]: .../bazel-out/k8-fastbuild-ST-54535d7cadf4/bin/my-test.runfiles/__main__/my-test
MYTEST ARGV[1]: x
MYTEST ARGV[2]: y
MYTEST ARGV[3]: z
MYTEST ARGV[4]: new arg
################################################################################

================================================================================

Known limitation:

bazel test :all --test_output=all --test_arg=a does not work as expected (--test_arg=a is ignored). This could be fixed with the approach shown under in the ../read_attr_in_transition example, but it is omitted here to not make this example overly complex.