Fixing uninitialized variable bug in blocking and PH joins

probe_side_eos_ was uninitialized at the first GetNext call and that was causing
random behavior. Also, PHJ GetNext() should init eos.

Change-Id: I586dd625cead11abac12cc007b16769a107b5746
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/3984
Reviewed-by: Ippokratis Pandis <ipandis@cloudera.com>
Tested-by: jenkins