fish: Don't fail if -m and --listen flags are both given (RHBZ#612178).

fish: Don't fail if -m and --listen flags are both given (RHBZ#612178).

Testing this against a Fedora disk image:

$ ./fish/guestfish --ro -a F13.img -m /dev/sda1 --listen
export GUESTFISH_PID=6033
$ ./fish/guestfish --remote=6033 -- ping-daemon
$ ./fish/guestfish --remote=6033 -- ping-daemon
$ ./fish/guestfish --remote=6033 -- exit

Without this fix the first remote command would fail because
qemu would have already been killed.

For stable-1.2 branch:
 - Cherry picked from commit 8161ea9bb046c8450384b5b15e1f4b2f3dca582b
 - Rebased for older guestfish code.