Revert "use built-in erlang:port_info to get os proc id"

This reverts commit e9d448efbcb15d22b0e706c4ff0d2b6e26e93f35.
port_info does not support os_pid until R15B02, and we're still on
R15B01.

/cc  @sdelano @seth  - reverts to the original fix, I'll be merging momentarily.