shill: Add new Manager property AlwaysOnVpnPackage

Defines the new constant. The property is a string
type and indicates the Android package name of the
VPN app that should be used for all traffic on
the chronos and debugd users.

BUG=b:72861260
TEST=unit tests

Change-Id: I882bd3c1ecd73b509e961adcda582a3142f025c3
Reviewed-on: https://chromium-review.googlesource.com/972403
Commit-Ready: Philipp Weiß <phweiss@chromium.org>
Tested-by: Philipp Weiß <phweiss@chromium.org>
Reviewed-by: Ben Chan <benchan@chromium.org>
1 file changed