isolate suite was not migrated to Dart 2

[mraleph]

When I try running it on VM I see a lot of failures on -c dartk --strong.

I am going to update status files.

@a-siva should this suite be migrated to Dart 2?

[a-siva]

We discovered that the isolate tests were migrated to lib_2/isolate during the migration process.
All the tests in tests/isolate directory should be skipped when running in dartk or dartkp modes.
@sivachandra is taking care of making the change to skip all tests in tests/isolate under dartk or dartkp modes.