shell: retry filer discovery until master knows a filer (#11989)

* shell: discover the filer on first use instead of at startup

The startup retry loop made every weed shell invocation wait out the
connect timeout on clusters that have no filer, even for commands that
only talk to the master. Discovery now runs once, on the first command
that actually needs a filer, keeping the retry-until-registered fix for
the fresh-cluster race without stalling master-only commands.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* shell: stop filer discovery retries on non-transient errors

A master that keeps answering ListClusterNodes with a permanent error
(permission denied, unimplemented) cannot gain a filer by retrying, so
discovery returns instead of polling until the deadline.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* shell: explain an empty filer list when discovery times out

* shell: retry filer discovery while the address is still empty

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

---------

Co-authored-by: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

weed/shell/command_remote_mount.go

@@ -85,7 +85,7 @@ func (c *commandRemoteMount) Do(args []string, commandEnv *CommandEnv, writer io
 	}
 
 	// find configuration for remote storage
-	remoteConf, err := filer.ReadRemoteStorageConf(commandEnv.option.GrpcDialOption, commandEnv.option.FilerAddress, remote_storage.ParseLocationName(*remote))
+	remoteConf, err := filer.ReadRemoteStorageConf(commandEnv.option.GrpcDialOption, commandEnv.FilerAddress(), remote_storage.ParseLocationName(*remote))
 	if err != nil {
 		return fmt.Errorf("find configuration for %s: %v", *remote, err)
 	}
@@ -133,7 +133,7 @@ func (c *commandRemoteMount) Do(args []string, commandEnv *CommandEnv, writer io
 func listExistingRemoteStorageMounts(commandEnv *CommandEnv, writer io.Writer) (mappings *remote_pb.RemoteStorageMapping, err error) {
 
 	// read current mapping
-	mappings, err = filer.ReadMountMappings(commandEnv.option.GrpcDialOption, commandEnv.option.FilerAddress)
+	mappings, err = filer.ReadMountMappings(commandEnv.option.GrpcDialOption, commandEnv.FilerAddress())
 	if err != nil {
 		return mappings, err
 	}