This change adds a dependency on lsof(1) when running on FreeBSD.
lsof(1) is not part of the base system, and lsof(1) would need to be
installed (usually from ports). If lsof(1) is not installed an error
will be returned in the form of:
ident_test.go:88: exec: "lsof": executable file not found in $PATH
Change-Id: I3cb15af369dc10a8a39aeaf82cceff3c788104b8