Store the value from BOARD_CUSTOM_BOOTIMG_MK to a file

This is needed so it can be read in when re-signing a package to
use the proper boot image.

Print notice when using a custom bootimage makefile

Change-Id: I6baab9f8964ce5d4fa9487f2859af9c385d7b21b
roomservice: Add recursive dependencies

Dependency repositories can now have dependencies themselves

Change-Id: I33a28709170da52bc98f4a62387927e3a11b2450
Merge remote-tracking branch 'github/cm-11.0' into cm11mod