Fix SSH deadlock during OutOfMemoryError

In close() method of SshFetchConnection and SshPushConnection
errorThread.join() can wait forever if JSch will not close the
channel's error stream.  Join with a timeout, and interrupt the
copy thread if its blocked on data that will never arrive.

Bug: 312863
Change-Id: I763081267653153eed9cd7763a015059338c2df8
Reported-by: Dmitry Neverov <dmitry.neverov@gmail.com>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>