Before this change we waited until until the timeout to check the
daemon was alive.
Now we check it every 100ms like we do the mount status.
This also fixes compiling on all platforms which was broken by the
previous change
9bfbf2a4a mount: fix macOS not noticing errors with --daemon
See: https://forum.rclone.org/t/rclone-mount-daemon-exits-successfully-even-when-mount-fails/43146
This patch will:
- add --daemon-wait flag to control the time to wait for background mount
- remove dependency on sevlyar/go-daemon and implement backgrounding directly
- avoid setsid during backgrounding as it can result in race under Automount
- provide a fallback PATH to correctly run `fusermount` under systemd as it
runs mount units without standard environment variables
- correctly handle ^C pressed while background process is being setting up
