Refactor NetworkUtils interaction with DHCP.

Separate out starting DHCP (DISCOVER) and RENEW operations from fetching
the results.  Add NetworkUtils.getDhcpResults(), to enable quick checks
of any available DhcpResults without extraneous interaction with the
DHCP daemon.

Bug: 19422416
Change-Id: I58808e529dda8429737e749f5caef56d923c0809
2 files changed