Add fsverity release cert

The release cert helps verifying CTS in a release build.

Bug: 153112812
Test: build, reboot, see a new key in /proc/keys
Change-Id: I6d8f4af6b1b0c023b668e81b7a1c71c7583d93d9
Merged-In: I6d8f4af6b1b0c023b668e81b7a1c71c7583d93d9