qemu-iotests: Don't create fifos / pidfiles with protocol paths

Trying to create, use, and remove fifos and pidfiles on protocol paths
(e.g. nfs://localhost/scratch/qemu-nbd.pid

) is obviously broken.

Use the local $TEST_DIR path before it is 'protocolized' for these
files.

Signed-off-by: Jeff Cody <jcody@redhat.com>
Message-id: bb4a731a35bc4ac81fe3db17479dd686315317c7.1485392617.git.jcody@redhat.com
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>