Ensure we can read a client root out of the trustStore

[mcpherrinm]

I just misconfigured a trustStoreType, and Keywhiz started, but I got strange client errors.

We should make sure the trustStore is sane, and bail if it isn't.

I had a JKS file, but told keywhiz it was a JCEKS file. (And, to round it off, I had named it .p12).