Hide Minitest's aggregated results if outputting inline.

We'd see the failures and errors reported after the run, which is needless, when we've already
reported them.

Turns:

```

.......................................S....................F

This failed

bin/rails test test/models/bunny_test.rb:14

....

Finished in 0.100886s, 1020.9583 runs/s, 1001.1338 assertions/s.

  2) Failure:
BunnyTest#test_something_failing [/Users/kasperhansen/Documents/code/collection_caching_test/test/models/bunny_test.rb:15]:
This failed

103 runs, 101 assertions, 1 failures, 0 errors, 1 skips

You have skipped tests. Run with --verbose for details.
```

Into:

```

...................S.......................................F

This failed

bin/rails test test/models/bunny_test.rb:14

......................

Finished in 0.069910s, 1473.3225 runs/s, 1444.7143 assertions/s.

103 runs, 101 assertions, 1 failures, 0 errors, 1 skips
```

1 files changed, 14 insertions, 0 deletions

diff --git a/railties/lib/rails/test_unit/minitest_plugin.rb b/railties/lib/rails/test_unit/minitest_plugin.rb
index 3a0a58df88..d1ba35a5ec 100644
--- a/railties/lib/rails/test_unit/minitest_plugin.rb
+++ b/railties/lib/rails/test_unit/minitest_plugin.rb
@@ -3,6 +3,16 @@ require "rails/test_unit/reporter"
 require "rails/test_unit/test_requirer"
 
 module Minitest
+  mattr_accessor(:hide_aggregated_results) { false }
+
+  module AggregatedResultSuppresion
+    def aggregated_results
+      super unless Minitest.hide_aggregated_results
+    end
+  end
+
+  SummaryReporter.prepend AggregatedResultSuppresion
+
   def self.plugin_rails_options(opts, options)
     opts.separator ""
     opts.separator "Usage: bin/rails test [options] [files or directories]"
@@ -38,6 +48,7 @@ module Minitest
       options[:fail_fast] = true
     end
 
+    options[:output_inline] = true
     options[:patterns] = opts.order!
   end
 
@@ -63,6 +74,9 @@ module Minitest
       Minitest.backtrace_filter = ::Rails.backtrace_cleaner if ::Rails.respond_to?(:backtrace_cleaner)
     end
 
+    # Disable the extra failure output after a run, unless output is deferred.
+    self.hide_aggregated_results = options[:output_inline]
+
     self.reporter << ::Rails::TestUnitReporter.new(options[:io], options)
   end