VPN: move VpnDialogs related methods into VpnConfig.

This might not be the best place for the glue code, but it is
known that choosing VpnBuilder will introduce a dependency
cycle of VpnBuilder, ConnectivityService, and the Vpn class.

Change-Id: I3f03617d1fe1a0b8fb3705c23265676fff51a75c
2 files changed