bisync: deglobalize to fix concurrent runs via rc - fixes #8675

Before this change, bisync used some global variables, which could cause errors
if running multiple concurrent bisync runs through the rc. (Running normally
from the command line was not affected.)

This change deglobalizes those variables so that multiple bisync runs can be
safely run at once, from the same rclone instance.

cmd/bisync/cmd.go

@@ -115,6 +115,7 @@ func (x *CheckSyncMode) Type() string {
 }
 
 // Opt keeps command line options
+// internal functions should use b.opt instead
 var Opt Options
 
 func init() {