Add remote:bitbucket-private to store private keys (OTA signing)

Change-Id: I8d8208bb785d8ad65f5daa2d8a5b5463c4ea7e27
Use TW_EXCLUDE_SUPERSU := true for ClamAV "ramdisk-recovery.img: Andr.Exploit.Ratc FOUND".

Change-Id: Iec657dc24b485a354841696961bc3bedb0f1d6bf