fuse: check mount point available before do runmount

1. Use more readable mount point information
2. Fix some typos

eg:

$ df -Th
Filesystem              Type            Size  Used Avail Use% Mounted on
localhost:8888:/        fuse.seaweedfs  206G   512  206G   1% /mnt/weedfs

$ mount | grep weedfs
localhost:8888:/ on /mnt/weedfs type fuse.seaweedfs (rw,nodev,relatime,user_id=0,group_id=0,default_permissions,allow_other)

Signed-off-by: Lei Liu <lei01.liu@horizon.ai>

weed/command/mount_freebsd.go

@@ -7,3 +7,7 @@ import (
 func osSpecificMountOptions() []fuse.MountOption {
 	return []fuse.MountOption{}
 }
+
+func checkMountPointAvailable(dir string) bool {
+	return true
+}