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_linux.go

@@ -1,6 +1,7 @@
 package command
 
 import (
+	"github.com/chrislusf/seaweedfs/weed/util"
 	"github.com/seaweedfs/fuse"
 )
 
@@ -9,3 +10,16 @@ func osSpecificMountOptions() []fuse.MountOption {
 		fuse.AllowNonEmptyMount(),
 	}
 }
+
+func checkMountPointAvailable(dir string) bool {
+	mountPoint := dir
+	if mountPoint != "/" && strings.HasSuffix(mountPoint, "/") {
+		mountPoint = mountPoint[0 : len(mountPoint)-1]
+	}
+
+	if mounted, err := util.Mounted(mountPoint); err != nil || mounted {
+		return false
+	}
+
+	return true
+}