Move global s3 opts into nova.image.s3

s3_host and s3_port are only used in nova.image.s3.

blueprint: scope-config-opts
Change-Id: Ia841406ebe7c03b2a58392e2453118e2646ad7ce
Move cert_topic into nova.cert.rpcapi

The cert_topic opt is only used in nova.cert.rpcapi and it makes sense
for the RPC module to "own" the topic option.

blueprint: scope-config-opts
Change-Id: If3584b8e1984e0425d9f33133f9d291739b04d49
Merge "Move global s3 opts into nova.image.s3"
Merge "Move cert_topic into nova.cert.rpcapi"