vendor_aicp: If SKIP_SIGNING is 1 we don't do the signing, which saves time for home builds.

Change-Id: I763d9b6444576a872fbd5c56bb2cf623ac2fa901
Merge "vendor_aicp: If SKIP_SIGNING is 1 we don't do the signing, which saves time for home builds." into kitkat
Merge branch 'kitkat' of https://github.com/AICP/vendor_aicp into HEAD