Fix hang when fetching over SSH

JSch may hang or abort with the timeout if JGit connects before
its obtained the streams.  Instead defer the connect() call until
after the streams have been configured.

Bug: 312383
Change-Id: I7c3a687ba4cb69a41a85e2b60d381d42b9090e3f
Reported-by: Dmitry Neverov <dmitry.neverov@gmail.com>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>