use recovery variant "philz" 

So that AOSP builders can keep both cwm and philz in their build path and build any one of them using the options
RECOVERY_VARIANT=cwm
or
RECOVERY_VARIANT=philz




with
CyanogenMod/android_build@c1b0bb6
and
CyanogenMod/android_build@6b21727
included now, we can have multiple recovery sources inside our build tree like
bootable/recovery-cm
bootable/recovery-twrp
bootable/recovery-philz

like that.

So that while building we can chose which recovery to include (or set separate recoveries for separate devices)