build: core: Parameterize recovery with a variant

Include extra vendor config early.  If RECOVERY_VARIANT is set, use it
to look for the recovery in an alternate path.

Change-Id: Iba54f0746d728c0dfeeb67b4d3166d5e25b1b5d7
tools: getb64key - print the base64 version of a PEM public key file

Change-Id: Ia94ff560c88dfe85c3fa55db5c8219aa0d3419ee
releasetools: Properly handle boot images that use dt

Instead of using a prebuilt boot/recovery image, bring the dt image
into the target files package and use it during package creation

Change-Id: I70ecf74423aad95a3eb8e085029c37450ae354a2

Conflicts:
	core/Makefile
	tools/releasetools/common.py