cmdMigrate: move vshConnect before vshWatchJob

cmdMigrate: move vshConnect before vshWatchJob

A possible fix to issue:
http://www.redhat.com/archives/libvir-list/2014-August/thread.html#00227

While doing migration on KVM host, found problem sometimes:
VM is already running on the target host and disappears from source
host, but 'virsh migrate' command line hangs, cannot exit normally.
If pressing "ENTER" key, it will exit.

The code hangs at tools/virsh-domain.c: cmdMigrate
->vshWatchJob->poll():
poll() is trying to select pipe_fd, which is used to receive message
from doMigrate thread. In debugging, found that doMigrate finishes
and at the end it does call safewrite() to write the retval ('0' or
'1') to pipe_fd, and the write is completed. But cmdMigrate poll()
cannot get the event. If pressing "ENTER" key, poll() can get the
event and select pipe_fd, then command line can exit.

In current code, authentication thread which is called by vshConnect
will use stdin, and at the same time, in cmdMigrate main process,
poll() is listening to stdin, that probably affect poll() to get
pipe_fd event. Better to move authentication before vshWatchJob. With
this change, above problem does not exist.

Signed-off-by: Chunyan Liu <cyliu@suse.com>