Add "client" section to router configs

[klingerf]

Once #73 ships, we'll have a few configuration options at the top level of our router config that are also available within the servers section of the same router config. The options at the top level apply to clients that are dynamically created by the router, whereas the options in the servers section apply to servers that are created when the router starts. For clarity, we should move the client-only top level options into a client config section.

Previously:

routers:
- protocol: thrift
  baseDtab: |
    /thrift => /io.l5d.fs/aservice;
  thriftFramed: false
  tls:
    kind: io.l5d.NoValidationTlsClient
  servers:
  - port: 4114
    ip: 0.0.0.0
    thriftFramed: false
    tls:
      certPath: /foo/cacert.pem
      keyPath: /foo/private/cakey.pem

Proposed future:

routers:
- protocol: thrift
  baseDtab: |
    /thrift => /io.l5d.fs/aservice;
  client:
    thriftFramed: false
    tls:
      kind: io.l5d.NoValidationTlsClient
  servers:
  - port: 4114
    ip: 0.0.0.0
    thriftFramed: false
    tls:
      certPath: /foo/cacert.pem
      keyPath: /foo/private/cakey.pem

[klingerf]

Maybe we should call the new section clients: instead of client:? I could go either way.

[olix0r]

i'd prefer client because in my mind plural "clients" means it's a list

[klingerf]

Yep, makes sense to me.

[wmorgan]

Nice to have in 0.0.10 but not critical.