keys: avoid duplicating recovery keys

Setting PRODUCT_EXTRA_RECOVERY_KEYS duplicates the default key and
makes it so we can't set an extra key earlier in the build

Change-Id: I239d9994d9ad40b1779877ea2e89b55bd02e4c00
Merge remote-tracking branch 'upstream/cm-11.0' into cm-11.0

Conflicts:
	core/Makefile
	tools/releasetools/ota_from_target_files

Change-Id: I6bd1fc69ed858a7daa02de6061669aabc97e05ad
Allow MINIGZIP override for default ramdisk compression tool

The Android build system only supports gzip for ramdisks, despite
the kernel itself supporting other options. Allow per-device
configs to specify their own tool, like so:

MINIGZIP := $(shell which lzma)
MINIGZIP := $(shell which bzip2)
...etc.

Change-Id: I0bc754bd2a73bfb4166228b420c8f013808c82f2