Improve lldb-mi tests. 

summary of changes:
  Cleanup: Use "line_number" API instead of hardcoded source lines
  Combine child.sendline with previous child.send command.
  test_lldbmi_tokens: Add test for MI tokens.
  test_lldbmi_badpathexe: Remove check for prompt so test for bad path can be enabled.

Patch from dawn@burble.org.



git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@222838 91177308-0d34-0410-b5e6-96231b3b80d8