Add initial lldb-mi tests.

Test 'test_lldbmi_interrupt' is only enabled for Darwin as
it seems to cause a timeout error on Linux.
Patch from dawn@burble.org.



git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@222750 91177308-0d34-0410-b5e6-96231b3b80d8