Fix race condition in test

This should fix travis. For real this time! This is the one!

The readpartial(100) meant that an earlier assert_stdout could chomp up
the output that a later assert_stdout wants, meaning that the later
assertion fails.

Reading only 1 byte at a time ensure that we don't read any more than is
necessary to verify the assertion.

railties/test/application/console_test.rb

@@ -106,13 +106,13 @@ class FullStackConsoleTest < ActiveSupport::TestCase
     teardown_app
   end
 
-  def assert_output(expected, timeout = 5)
+  def assert_output(expected, timeout = 1)
     timeout = Time.now + timeout
 
     output = ""
     until output.include?(expected) || Time.now > timeout
       if IO.select([@master], [], [], 0.1)
-        output << @master.readpartial(100)
+        output << @master.read(1)
       end
     end