Since the tailscaled binaries that we distribute are static and don't
link cgo, we previously wouldn't fetch group IDs that are returned via
NSS. Try shelling out to the 'id' command, similar to how we call
'getent', to detect such cases.
Updates #11682
Signed-off-by: Andrew Dunham <andrew@du.nham.ca>
Change-Id: I9bdc938bd76c71bc130d44a97cc2233064d64799
