core: Allow to disable block based OTA's

on Xiaomi Mi2, it causes that the user can't install GAPPS because
the filesystem is smaller than the partition then(users resize the syspart).


to use old style of output add this to boardconfig of device tree: 
TARGET_USES_BLOCK_BASED_OTA := false

Change-Id: I1dcde9c9a212c34108629537cb8c1088a0373573
build: add color to chromium prebuilt check message

Change-Id: I1063dc744f7f6ab618e10c9e3b5132af1cbab490
Use -O3 flag
Update roomservice.py