Squash commits from CM for making lunch faster

before patch:
time lunch aokp_d2tmo-userdebug
real	0m33.123s

after patch:
time lunch aokp_d2tmo-userdebug
real	0m3.575s

Load only the current product config makefile.

To reduce the start time.
With the change and previous change of doing clean step in only given paths,
start time of mm/mmm is reduced from ~5s to about 1s;
lunch time is reduced from ~40s to 3.5s.

Bug: 7186768,7169854
Change-Id: Ifd72ba1c6362a5e1125a23c505fd47947ab56675

build: Fix fastpath code for AOKP

 * We need to adjust to the new validations

Change-Id: I9066d4f437beb9597027ee6bbb52504b5e7e84c5

build: Preliminary support for CM product builds

If building a cm_* product, skip crawling the filesystem for
AndroidProduct makefiles (and, of course, parsing their contents)
and aim directly for the device/cm/<product> device configuration

Change-Id: I2a5e70dda973a6fcdbba0d5e26b35b99d3f1aea2

Change how we search for CM makefiles.

build: Fix fastpath code for CM_BUILD

 * We need to adjust to the new validations

Change-Id: I9066d4f437beb9597027ee6bbb52504b5e7e84c5

build: export RB_BUILD

reference RB_BUILD

Change-Id: I95d9f05c622e74117cda0967cf6cf248a68e56c5