Tweak emulator support.

Use shell stop and start instead of reboot.
Create a tmp sdk home instead of reusing build dir which may be static.
Add an option to skip wifi setup.
Add option to allow setting system props when launching emulator.

Bug: 12962914

Change-Id: Ie763519b21ca2001a94f8160a75a6893f2be1b7e
3 files changed