DERBY-6704 Hang in AutoloadTest.spawnProcess:JDBCDriversEmbeddedTest on Mac/jdk7,8

Diagnostic patch to print the output of stderr and stdout from the
subprocesses if one of "derby.tests.{trace,debug}" is true.

git-svn-id: https://svn.apache.org/repos/asf/db/derby/code/trunk@1617825 13f79535-47bb-0310-9956-ffa450edef68