Limit the number of test cases to try to 100

Test driver runner would previously hang for test drivers that do not
properly terminate -- returning -1 to indicate the one-past-last test case.
Interleave stderr and stdout of test drivers.

stderr was printed after stdout, making it difficult to determine when
an error message was printed.
Add decorators for test driver outputs.

Add decorators for test driver outputs similar to those for compiler and
linker warnings and errors to simply parsing by continuous integration
tools.
Stop buffering stdout and stderr for test outputs.

Test outputs were not properly interleaved -- stderr from the runner
runner utility were shown before stderr from the test driver itself.
Show build timer when some unit tests fail.

Also remove an unused block of code from bdeunittest.py.
Add .arcconfig to enable Phabricator reviews
Constraining Waf to only look for the supported versions of Python