This set of changes addresses the issue I described in Bug 23403, in short most LLDB-MI tests fail unexpectedly due to timeout on my Ubuntu 14.10 x86_64 VirtualBox VM. I have no idea why the Ubuntu buildbots don't seem to suffer from this issue. This patch just makes MiTestCaseBase.spawnLldbMi() block until the spawned LLDB-MI child process outputs the (gdb) prompt, which ensures that MI commands aren't sent to the LLDB-MI child process until it's ready.
Before these changes 52 LLDB-MI tests failed unexpectedly (all but one due to timeouts), after these changes no tests fail due to timeouts. I still get one unexpected failure in test_lldbmi_source_option_start_script_error in TestMiStartupOptions.py, but that's due to a file error, that test should be skipped on Linux just like the other two start_script tests until the file error is fixed.