This allows us to use the same PKCS#11 key for both cert signing and OCSP
signing, and simplifies config and startup.
This also starts building with -tags pkcs11 in all scripts, which is required
now that the CA can choose between pkcs11 and non-pkcs11.
In order to successfully issue using a pkcs11 key, you'll need to run a version
of Go built off the master branch. The released versions are missing this
commit:
fe40cdd756,
which is necessary for PKCS#11 signing.