Some minor cleanup for the customer_testing shard (#49501)
Some minor cleanup for the customer_testing shard (#49501)

* Allow projects that don't have tests on every platform.
  We don't really need to enforce that random projects have
  tests on every platform.

* Add some text at the end of the shard so we know it's
  actually running all the tests.
tvolkert/flutter,tvolkert/flutter,flutter/flutter,cbracken/flutter,flutter/flutter,tvolkert/flutter,cbracken/flutter,cbracken/flutter,tvolkert/flutter,Hixie/flutter,cbracken/flutter,Hixie/flutter,cbracken/flutter,flutter/flutter,tvolkert/flutter,cbracken/flutter,flutter/flutter,Hixie/flutter,Hixie/flutter,flutter/flutter,Hixie/flutter,tvolkert/flutter,tvolkert/flutter,Hixie/flutter,cbracken/flutter,Hixie/flutter,flutter/flutter,flutter/flutter,flutter/flutter,flutter/flutter,Hixie/flutter,cbracken/flutter,tvolkert/flutter,Hixie/flutter,tvolkert/flutter,cbracken/flutter,Hixie/flutter,flutter/flutter,tvolkert/flutter,cbracken/flutter