Check swift.conf MD5 with recon

I've seen several folks recently have problems with their Swift
clusters because they had different hash prefixes on different
nodes. Let's help them out by having recon check that.

Note that MD5-equality is stronger than what we need (which is
ConfigParser-equality for a particular set of keys), but this way we
don't expose the secret hash prefix and suffix across the internal
network, just the MD5 checksum of the file containing them.

Change-Id: I3af984ee45947345891b3c596a88e3464f178cc7
Merge "Check swift.conf MD5 with recon"