mountlib: correctly daemonize for compatibility with automount - #5593

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

go.mod

@@ -37,7 +37,6 @@ require (
 	github.com/jcmturner/gokrb5/v8 v8.4.2
 	github.com/jlaffaye/ftp v0.0.0-20210307004419-5d4190119067
 	github.com/jzelinskie/whirlpool v0.0.0-20201016144138-0675e54bb004
-	github.com/kardianos/osext v0.0.0-20190222173326-2bc1f35cddc0 // indirect
 	github.com/klauspost/compress v1.13.4
 	github.com/koofr/go-httpclient v0.0.0-20200420163713-93aa7c75b348
 	github.com/koofr/go-koofrclient v0.0.0-20190724113126-8e5366da203a
@@ -56,7 +55,6 @@ require (
 	github.com/prometheus/procfs v0.7.3 // indirect
 	github.com/putdotio/go-putio/putio v0.0.0-20200123120452-16d982cac2b8
 	github.com/rfjakob/eme v1.1.2
-	github.com/sevlyar/go-daemon v0.1.5
 	github.com/shirou/gopsutil/v3 v3.21.8
 	github.com/sirupsen/logrus v1.8.1
 	github.com/skratchdot/open-golang v0.0.0-20200116055534-eef842397966