shill: Pass a parameter to dhcp client to request a hostname

This will enable dynamic DNS, or at the very least allow DHCP
requests to be identified and distinguished at the server side.

BUG=chromium-os:23741
TEST=New unit tests monitor hostname arg passed to dhcpcd,
and to assure values are being loaded/saved.  Also double
checked on real system by doing a dbus-send to set manager.HostName
and checked that the name was persisted, and that the next
DHCP server we connected to stored this hostname.
CQ-DEPEND=Ic807a2235e0cdcb32a08f9c2c760a86c3579431c

Change-Id: Ic127b65d8563b15e55549a0f029385d0632eaf6c
Reviewed-on: https://gerrit.chromium.org/gerrit/14045
Reviewed-by: Paul Stewart <pstew@chromium.org>
Tested-by: Paul Stewart <pstew@chromium.org>
Commit-Ready: Paul Stewart <pstew@chromium.org>
diff --git a/mock_dhcp_config.cc b/mock_dhcp_config.cc
index 1ff551d..4d2cf4d 100644
--- a/mock_dhcp_config.cc
+++ b/mock_dhcp_config.cc
@@ -10,11 +10,13 @@
                                EventDispatcher *dispatcher,
                                DHCPProvider *provider,
                                const std::string &device_name,
+                               const std::string &request_host_name,
                                GLib *glib)
     : DHCPConfig(control_interface,
                  dispatcher,
                  provider,
                  device_name,
+                 request_host_name,
                  glib) {}
 
 MockDHCPConfig::~MockDHCPConfig() {}