mount: add -volumeName to name the disk explicitly (#11165)

* mount: let volumeName take an explicit override

volumeName only ever derived the disk's label from -filer.path, -dir,
or the filer address, so a name that happened to collide with
something else - e.g. a UNC share's own name - could not be changed
without moving what was mounted. Give it an override parameter that
wins over all three; nothing passes one yet.

* mount: add -volumeName to name the disk explicitly

Windows has no equivalent of the "weed fuse" -o passthrough that lets
a Linux or macOS mount override its derived volname, so a name picked
up from -dir - e.g. a UNC share's own name - could not be changed
short of moving what was mounted. -volumeName overrides it on every
platform.

* mount: document -volumeName

* mount: scope -volumeName's help text to macOS and Windows

Linux has no volume-label mount option for -volumeName to feed, so
the flag's own description says where it applies instead of leaving
that unstated.

* mount: forward -volumeName through the weed fuse option parser

weed fuse (the /etc/fstab helper) turns -o key=value into the same
MountOptions weed mount takes, but volumeName had no case, so it fell
through to being forwarded as a literal, unrecognized FUSE option
instead of ever reaching mountOptions.volumeName.

* mount: apply -volumeName to FsName on Linux and FreeBSD

FsName only ever took the filer address and -filer.path, so
-volumeName had nothing to override there and silently did nothing;
the skipAutofs case still forces "fuse", since that name is what
util-linux/mount requires to recognize the pseudo filesystem.

weed/command/mount_common.go

@@ -278,10 +278,14 @@ func resolveCacheDirs(option *MountOptions) (string, string) {
 }
 
 // volumeName labels the mount where the platform shows one, in Finder and in
-// Explorer. The mounted path names the disk, then the mount point; the filer
-// address, which every mount from one filer shares, is the last resort.
-func volumeName(filer, filerMountRootPath, dir string) string {
-	name := lastSegment(filerMountRootPath)
+// Explorer. An explicit override always wins; failing that, the mounted path
+// names the disk, then the mount point; the filer address, which every mount
+// from one filer shares, is the last resort.
+func volumeName(filer, filerMountRootPath, dir, override string) string {
+	name := override
+	if name == "" {
+		name = lastSegment(filerMountRootPath)
+	}
 	if name == "" {
 		name = lastSegment(dir)
 	}