Verify the disk file exists before running qemu-img on it.

Should resolve bug 955788, although it is a little hard to tell
because the bug is so old.

Change-Id: Ic0c47f4b6181f56a98cf58d4ebe2cc926d06d524
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
Move network_topic into nova.network.rpcapi

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

blueprint: scope-config-opts
Change-Id: Icd779f34df47ac6dd048b3e41995e872d8859872
Move console_topic into nova.console.rpcapi

Even though the console_topic opt is used outside nova.console.rpcapi,
it makes sense for the RPC module to "own" the topic option.

blueprint: scope-config-opts
Change-Id: I0f00927ca1c0bba7b21315240165e83e7075ebb7
Move scheduler_topic into nova.scheduler.rpcapi

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

blueprint: scope-config-opts
Change-Id: Iafb8705eb716b650b63e060fe1dd36666bcee812
Merge "Verify the disk file exists before running qemu-img on it."
Merge "Move global s3 opts into nova.image.s3"
Merge "Move cert_topic into nova.cert.rpcapi"
Merge "Move network_topic into nova.network.rpcapi"
Merge "Move console_topic into nova.console.rpcapi"
Merge "Move scheduler_topic into nova.scheduler.rpcapi"