Fix flaky t_restart_previous_consumers testcase

[k32]

%%% brod_client_SUITE: .......

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brod_client_SUITE:t_restart_previous_consumers failed on line 271

Reason: {badmatch,{error,{consumer_not_found,<<"brod-client-SUITE-to...}

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Testing lib.brod: *** FAILED test case 12 of 83 ***

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2020-03-25 17:25:52.704

=== t_restart_previous_consumers begin ===

=INFO REPORT==== 25-Mar-2020::17:25:52.705429 ===

    supervisor: {local,brod_sup}

    started: [{pid,<0.2251.0>},

              {id,t_restart_previous_consumers},

              {mfargs,{brod_client,start_link,

                                   [[{"localhost",9092}],

                                    t_restart_previous_consumers,[]]}},

              {restart_type,{permanent,10}},

              {shutdown,5000},

              {child_type,worker}]

=INFO REPORT==== 25-Mar-2020::17:25:52.708933 ===

    supervisor: {<0.2254.0>,brod_consumers_sup}

    started: [{pid,<0.2255.0>},

              {id,<<"brod-client-SUITE-topic">>},

              {mfargs,

                  {supervisor3,start_link,

                      [brod_consumers_sup,

                       {brod_consumers_sup2,<0.2251.0>,

                           <<"brod-client-SUITE-topic">>,[]}]}},

              {restart_type,{permanent,10}},

              {shutdown,infinity},

              {child_type,supervisor}]

=INFO REPORT==== 25-Mar-2020::17:25:52.709064 ===
    supervisor: {<0.2255.0>,brod_consumers_sup}
    started: [{pid,<0.2256.0>},
              {id,0},
              {mfargs,{brod_consumer,start_link,
                                     [<0.2251.0>,
                                      <<"brod-client-SUITE-topic">>,0,[]]}},
              {restart_type,{transient,2}},
              {shutdown,5000},
              {child_type,worker}]

----------------------------------------------------
2020-03-25 17:25:52.710
=== t_restart_previous_consumers end ===
%%% brod_client_SUITE ==> t_restart_previous_consumers: FAILED
%%% brod_client_SUITE ==> {{badmatch,{error,{consumer_not_found,<<"brod-client-SUITE-topic">>}}},
 [{brod_client_SUITE,t_restart_previous_consumers,1,
                     [{file,"/home/travis/build/klarna/brod/test/brod_client_SUITE.erl"},
                      {line,271}]},
  {test_server,ts_tc,3,[{file,"test_server.erl"},{line,1748}]},
  {test_server,run_test_case_eval1,6,[{file,"test_server.erl"},{line,1263}]},
  {test_server,run_test_case_eval,9,[{file,"test_server.erl"},{line,1195}]}]}```