diagnostics for jps output
diagnostics for jps output

Summary:
I have no idea why `buck killall` might fail, so I added diagnostics
when parsing of `jps -l` output.

Test Plan:
Build package and execute:

`./buck-out/gen/programs/buck.pex killall`

Still works fine me.

Then replace `if len(split) != 2:` with `if len(split) != 3:` and
execute that command again:

```
2018-02-12 13:29:24,076 [ERROR][buck.py:115] cannot parse a line in jps -l outout: '20053 sun.tools.jps.Jps\n'
Traceback (most recent call last):
  File "programs/buck.py", line 89, in <module>
    exit_code = main(sys.argv, reporter)
  File "programs/buck.py", line 56, in main
    return killall_buck(reporter)
  File "programs/buck.py", line 33, in killall_buck
    raise Exception('cannot parse a line in jps -l outout: ' + repr(line))
Exception: cannot parse a line in jps -l outout: '20053 sun.tools.jps.Jps\n'
```

Reviewed By: dinhviethoa

fbshipit-source-id: 776824a

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