Partest mark test that timed out as skipped instead of failed

[smarter]

See https://scala-ci.typesafe.com/job/dotty-master-validate-partest/1128/console the tests finished with:

[error] Interrupted waiting for command to finish (java -Xms64M -Xmx1024M ...)
[info] Thread pool timeout elapsed before all tests were complete!!!
646 - run/t6253a.scala                          [non-zero exit code]
[info] 
[info] 1504/1505 passed, 1 skipped (elapsed time: 04:11:41)
[info] Test Run PASSED
[success] Total time: 15105 s, completed Feb 23, 2016 4:00:29 PM

which means that from the github ui this failure is completely silent.

[som-snytt]

Fails tests in the current category, but just skips subsequent categories. The bookkeeping could be improved.

#85

[SethTisue]

closing old scala-partest issues that seem unlikely to get noticed here now that we've re-in-sourced. could be revived under scala/scala-dev