Improve test harness for the buildbots

- Add a "parsable" mode to dotest.py that outputs test results in exactly the same format as clang's lit tests
- Improve dosep script to output list of failing tests (output should look like clang test failure summaries)
- Cleanup lldb/test/Makefile to remove needless parameters and environment variables
- Switch makefile tests to use parsable-mode output; should make the buildbot results parsable
- Switch makefile tests to use dosep to log catch crashing tests (instead of halting the test suite)

llvm-svn: 175309