Added the test for UID field of NetwrokDnsEventReported atom

Bug: 309575211
Test: atest resolv_unit_test, resolv_stats_test_utils_test
      statsd_testdrive

Metrics dump:
  event_type: EVENT_GETADDRINFO,
  return_code: RC_EAI_NO_ERROR,
  latency_micros: 105375,
  hints_ai_flags: 1024,
  res_nsend_flags: -1,
  network_type: NT_CELLULAR,
  private_dns_modes: PDM_OPPORTUNISTIC,
  dns_query_events: {
    dns_query_event:   [{
      rcode: NS_R_NO_ERROR,
      type: NS_T_AAAA,
      cache_hit: CS_NOTFOUND,
      ip_version: IV_IPV6,
      protocol: PROTO_UDP,
      retry_times: 0,
      dns_server_index: 0,
      latency_micros: 98227,
      linux_errno: SYS_NO_ERROR
    },{
      rcode: NS_R_NO_ERROR,
      type: NS_T_A,
      cache_hit: CS_NOTFOUND,
      ip_version: IV_IPV6,
      protocol: PROTO_UDP,
      retry_times: 0,
      dns_server_index: 0,
      latency_micros: 101843,
      linux_errno: SYS_NO_ERROR
    }]
  },
  sampling_rate_denom: 400,
  uid: 10230

Change-Id: I113e1671ae28feed8751afd720743bc0f6745e3b