Set the test suite for Robolectric tests

Mark Robolectric tests as belonging to the `robolectric-tests` suite
since tools expect test modules to belong to at least one suite.
Note that tests not marked with a suite implicitly get annotated with
the `null-suite`.

This is also required for Atest Bazel mode which only includes files of
test modules with a non-empty suite attribute in the Tradefed test
directory.

See aosp/2181295 for more details.

Test: m out/target/product/vsoc_x86_64/module-info.json
Bug: 222437352
Bug: 228799625
Change-Id: I9dedaf1661a351c32d2affbaf1f9b89d672acc3a