rabbit_mgmt_http_SUITE: update test suite shard count

Author: michaelklishin

deps/rabbitmq_management/BUILD.bazel

@@ -167,7 +167,7 @@ rabbitmq_integration_suite(
     additional_beam = [
         "test/rabbit_mgmt_runtime_parameters_util.beam",
     ],
-    shard_count = 2,
+    shard_count = 6,
     runtime_deps = [
         "//deps/amqp10_client:erlang_app",
     ],