test/blobfs: add 1 second delay before checking the mount point

The thread loop function fuse_loop_new_thread() may not be executed
before checking the mount point.

For #1572 case, only one notice log as follow:
"Mounting filesystem on bdev BlobfsBdev to path /tmp/spdk_tmp_mount..."

For normal cases, there are two notice messages:
"Mounting filesystem on bdev BlobfsBdev to path /tmp/spdk_tmp_mount..."
"blobfs_fuse.c: 267:fuse_loop_new_thread: NOTICE: Start to loop blobfs..."

So add 1 second delay here.

Change-Id: I8f36fa538cb8864c94fe8110ced38703b7e2e413
Signed-off-by: Changpeng Liu <changpeng.liu@intel.com>
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/4260
Community-CI: Broadcom CI
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>
Reviewed-by: Ben Walker <benjamin.walker@intel.com>
Reviewed-by: Shuhei Matsumoto <shuhei.matsumoto.xt@hitachi.com>

test/blobfs/blobfs.sh

@@ -94,6 +94,8 @@ function blobfs_fuse_test() {
 	# So directly use default sock path.
 	waitforlisten $blobfs_pid /var/tmp/spdk.sock
 
+	sleep 1
+
 	# check mount status
 	mount | grep "$mount_dir"