Settings: Expose option to change the device hostname.

This adds an option to modify the device hostname used
in ip resolution. This is useful when connecting to the
android device in a dynamic dhcp environment.

Change-Id: I1d8302f06144dbb3e6ddba68594cc5718b4f0bb7
(based on commit Ibc145b74036617248d4f33c6866cc9c8a8cc8974)