Build: Add support for specifying build variant in brunch/breakfast
Build: Add support for specifying build variant in brunch/breakfast

This little modification allows specifying build variant in brunch/
breakfast commands. For example we can use "brunch shamu user" to build
user variant instead of default user.

When no extra argument is given, userdebug is default.

Change-Id: If4169cee368aadd52996c34846b62aeadc2b0ff3

xorware/android_build,xorware/android_build,xorware/android_build,xorware/android_build,xorware/android_build