ruby: more flexible ruby tester support

ruby: more flexible ruby tester support

This patch allows the ruby random tester to use ruby ports that may only
support instr or data requests.  This patch is similar to a previous changeset
(8932:1b2c17565ac8) that was unfortunately broken by subsequent changesets.
This current patch implements the support in a more straight-forward way.
Since retries are now tested when running the ruby random tester, this patch
splits up the retry and drain check behavior so that RubyPort children, such
as the GPUCoalescer, can perform those operations correctly without having to
duplicate code.  Finally, the patch also includes better DPRINTFs for
debugging the tester.