Add -exec-abort command (MI); Don't exit on eStateExited

Summary:
Add -exec-abort command + test.

Also, I had fixed an error, when lldb-mi exits on eStateExited. With current patch we can re-run target:
```
-file-exec-and-symbols hello
^done
-exec-run
^running
*stopped,reason="breakpoint-hit"...
-exec-abort
^done
*stopped,reason="exited-normally"...    <- program exits
-exec-run                               <- run again
^running
*stopped,reason="breakpoint-hit"...
```

All tests pass on OS X.

Reviewers: zturner, emaste, abidh, clayborg

Reviewed By: abidh, clayborg

Subscribers: lldb-commits, emaste, zturner, clayborg, abidh

Differential Revision: http://reviews.llvm.org/D7794

llvm-svn: 230321