Add compliance tests for IPv4 entries, fix server defect.

[robshakir]

  * (M) client/client.go
    - Improve logging.
  * (M) compliance/compliance.go
    - Add test for adding IPv4 entry in a single ModifyRequest,
     and within separate requests.
  * (M) fluent/fluent.go
    - Add support for WithIPAddress to builder.
  * (M) gnmit/gnmit.go
    - Minor refactor to use a new GNMIServer container - no-op
    change for adding gNMI Set support.
  * (M) rib/rib.go
    - Improve logging.
  * (M) server/server.go
  * (M) server/server_test.go
    - Resolve a defect whereby the server called modifyEntry within
      a goroutine per operation within a ModifyRequest. In the case
      where a single ModifyRequest made multiple entries resolvable,
      then an entry could be duplicate ACK'd, by all the entries that
      made it resolvable. Whilst the RIB is safe to modify in this
      manner, the pending queue could result in this occurring - the
      duplicate install is a NOOP, but the duplicate ACK violated the
      API contract. Initially, resolve this issue by serially processing
      modify requests - added a TODO to cover a less naive solution.

[robshakir]

@liulk - PTAL, I merged your changes to take the stub as an argument here.