[lldbtests] Handle errors instead of crashing.
[lldbtests] Handle errors instead of crashing.

If you pass an invalid compiler/debugger path on the cmdline to `dotest.py`  this is what you get.

  Traceback (most recent call last):
  [...]
    File "dotest.py", line 7, in <module>
      lldbsuite.test.run_suite()
  [...]

And with the patch applied:

  /home/davide/work/build-lldb/bin/clandasfasg is not a valid path, exiting

Differential Revision:  https://reviews.llvm.org/D39199

git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@316393 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb,llvm-mirror/lldb,apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb,apple/swift-lldb,llvm-mirror/lldb,llvm-mirror/lldb