Stop management application if metrics collection is disabled

[dcorbacho]

Depends on rabbitmq/rabbitmq-management-agent#78

[#164376052]

Types of Changes

• Bugfix (non-breaking change which fixes issue #NNNN)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation (correction or otherwise)
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Checklist

• I have read the CONTRIBUTING.md document
• I have signed the CA (see https://cla.pivotal.io/sign/rabbitmq)
• All tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• Any dependent changes have been merged and published in related repositories

Further Comments

If this is a relatively large or complex change, kick off the
discussion by explaining why you chose the solution you did and what
alternatives you considered, etc.

[gerhard]

Given the following rabbitmq.conf

management_agent.disable_metrics_collector = true

If rabbitmq_management plugin is enabled before the node is booted, the node will fail to boot with the following error:

BOOT FAILED
===========

Error description:
    init:do_boot/3
    init:start_em/1
    rabbit:start_it/1 line 464
    rabbit:broker_start/1 line 340
    rabbit:start_loaded_apps/2 line 580
    app_utils:manage_applications/6 line 126
    lists:foldl/3 line 1263
    rabbit:'-handle_app_error/1-fun-0-'/3 line 703
throw:{could_not_start,rabbitmq_management,
          {rabbitmq_management,
              {"Metrics collection disabled in management agent",
               {rabbit_mgmt_app,start,[normal,[]]}}}}
Log file(s) (may contain more information):
   /var/folders/d6/dt_lc3pn5qg8wd93w_tgmx7c0000gn/T/rabbitmq-test-instances/rabbit/log/rabbit.log
   /var/folders/d6/dt_lc3pn5qg8wd93w_tgmx7c0000gn/T/rabbitmq-test-instances/rabbit/log/rabbit_upgrade.log

{"init terminating in do_boot",{could_not_start,rabbitmq_management,{rabbitmq_management,{"Metrics collection disabled in management agent",{rabbit_mgmt_app,start,[normal,[]]}}}}}
init terminating in do_boot ({could_not_start,rabbitmq_management,{rabbitmq_management,{Metrics collection disabled in management agent,{rabbit_mgmt_app,start,[_]}}}})
gmake: *** [/Users/gerhard/github.com/rabbitmq/3.8-prometheus/deps/rabbit_common/mk/rabbitmq-run.mk:251: run-broker] Error 1

If enabling rabbitmq_management when this config option is set to true, we get the following expected error:

Enabling plugins on node rabbit@55e482b3fabb:
rabbitmq_management
The following plugins have been configured:
  rabbitmq_management
  rabbitmq_management_agent
  rabbitmq_prometheus
  rabbitmq_web_dispatch
Applying plugin configuration to rabbit@55e482b3fabb...
** (CaseClauseError) no case clause matching: {:could_not_start, :rabbitmq_management, {:rabbitmq_management, {'Metrics collection disabled in management agent', {:rabbit_mgmt_app, :start, [:normal, []]}}}}
    (rabbitmqctl) lib/rabbitmq/cli/plugins/plugins_helpers.ex:218: RabbitMQ.CLI.Plugins.Helpers.update_enabled_plugins/2
    (rabbitmqctl) lib/rabbitmq/cli/plugins/plugins_helpers.ex:115: RabbitMQ.CLI.Plugins.Helpers.update_enabled_plugins/4
    (rabbitmqctl) lib/rabbitmq/cli/plugins/commands/enable_command.ex:104: anonymous fn/6 in RabbitMQ.CLI.Plugins.Commands.EnableCommand.do_run/2
    (elixir) lib/stream.ex:1311: anonymous fn/2 in Stream.iterate/2
    (elixir) lib/stream.ex:1497: Stream.do_unfold/4
    (elixir) lib/stream.ex:1568: Enumerable.Stream.do_each/4
    (elixir) lib/stream.ex:936: Stream.do_enum_transform/7
    (elixir) lib/stream.ex:1568: Enumerable.Stream.do_each/4