Show expiry warning when running on Android 4

After a set date a snackbar is shown, warning that Briar will stop
working at a later set date.
3 jobs for !1577 with 2251-warn-briar-expires-on-android4 in 9 minutes and 40 seconds (queued for 5 seconds)
latest detached
Status Name Job ID Coverage
  Test
passed test #14739

00:09:40

 
  Optional Tests
manual android test #14740
kvm allowed to fail manual
manual bridge test #14741
allowed to fail manual