wire timeouts and exceptional inferior process exits through the test event system

The results formatter system is now fed timeouts and exceptional process
exits (i.e. inferior dotest.py process that exited by signal on POSIX
systems).

If a timeout or exceptional exit happens while a test method is running
on the worker queue, the timeout or exceptional exit is charged and
reported against that test method.  Otherwise, if no test method was
running at the time of the timeout or exceptional exit, only the test
filename will be reported as the TIMEOUT or ERROR.

Implements:
https://llvm.org/bugs/show_bug.cgi?id=24830
https://llvm.org/bugs/show_bug.cgi?id=25703

In support of:
https://llvm.org/bugs/show_bug.cgi?id=25450

llvm-svn: 255097