OS X: fix lsof helper
OS X: fix lsof helper

This changes the command for getting the process tree on OS X to use 'pstree',
since the OS X version of 'ps' is quite limited. This adds an additional
'pstree' Homebrew package requirement for running the server processes on OS X.
We could figure out how pstree works on mac, but it's probably not worth the
effort.

Change-Id: I21bc5b4bb091385e16ef994819a9b0e751387de7
Reviewed-on: http://gerrit.cloudera.org:8080/1362
Tested-by: Internal Jenkins
Reviewed-by: Todd Lipcon <2c763d726a8c2f6afda9be7e0e56a2caa6bb5e6b@cloudera.com>

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