Fixed inconsistency between HasIntField and IntField (#2813)

plugins/inputs/aerospike/aerospike_test.go

plugins/inputs/http_response/http_response_test.go

plugins/inputs/memcached/memcached_test.go

plugins/inputs/mongodb/mongodb_data_test.go

plugins/inputs/mongodb/mongodb_server_test.go

plugins/inputs/ping/ping_windows_test.go

plugins/inputs/postgresql/postgresql_test.go

...nputs/postgresql_extensible/postgresql_extensible_test.go

plugins/inputs/powerdns/powerdns_test.go

plugins/inputs/rabbitmq/rabbitmq_test.go

plugins/inputs/rethinkdb/rethinkdb_data_test.go

plugins/inputs/system/processes_test.go

plugins/inputs/zookeeper/zookeeper_test.go

testutil/accumulator.go