qemu-iotests: Fix paths for NFS

Test cases were trying to use nfs:// URLs as local filenames, which made
every test fail for NFS. With TEST_IMG and TEST_IMG_FILE set like for
the other protocols, NFS tests can pass again.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>

tests/qemu-iotests/common.rc

@@ -147,8 +147,8 @@ else
         TEST_IMG_FILE=$TEST_DIR/t.$IMGFMT
         TEST_IMG="ssh://127.0.0.1$TEST_IMG_FILE"
     elif [ "$IMGPROTO" = "nfs" ]; then
-        TEST_DIR="nfs://127.0.0.1/$TEST_DIR"
-        TEST_IMG=$TEST_DIR/t.$IMGFMT
+        TEST_IMG_FILE=$TEST_DIR/t.$IMGFMT
+        TEST_IMG="nfs://127.0.0.1$TEST_IMG_FILE"
     elif [ "$IMGPROTO" = "vxhs" ]; then
         TEST_IMG_FILE=$TEST_DIR/t.$IMGFMT
         TEST_IMG="vxhs://127.0.0.1:9999/t.$IMGFMT"