Review all communication on stdout/stderr between jtreg and JVMs

In the game of JEP 400 (UTF-8 by default) we should review all use of stdout and stderr between jtreg and all JVMs it execs. This includes agent VMs, VMs for "otherVM tests" and the startup JVMs used to gather info (properties) from the test JVM.

Perhaps as a working hypothesis, all significant communication should be done on private sockets (i.e. not stdout/stderr) and just "safely" log any activity on stdout/stderr.

Maybe while collecting info (properties) we can determine the encoding in use for stdout/stderr so that jtreg can react accordingly.