Fix color-related test failures

The `red`, `yellow`, etc. helpers within `formatter_test.rb` are
specifically used only for testing logfile output, not console output.
Since color is not present in logfile output for SSHKit > 1.7.1, these
helpers essentially do nothing in the latest SSHKit.

Therefore, when asserting color console output, it is necessary to use
the actual ANSI color control codes, as this commit does in the
`test_log_message_levels`. Note that tests that require color must
explicitly turn on color using `airbrussh_config.color = true`.

I removed the color expectations from `test_handles_rake_tasks`, since
color is not enabled for that test.

test/airbrussh/formatter_test.rb

@@ -245,15 +245,15 @@ def test_handles_rake_tasks
       "      02 command 2\n",
       /    ✔ 02 #{@user_at_localhost} \d.\d+s\n/,
       "00:00 special_rake_task_2\n",
-      "      #{red('ERROR')} New task starting\n",
+      "      ERROR New task starting\n",
       "00:00 special_rake_task_3\n",
       "      01 echo command 3\n",
       "      01 command 3\n",
       /    ✔ 01 #{@user_at_localhost} \d.\d+s\n/,
       "      02 echo command 4\n",
       "      02 command 4\n",
       /    ✔ 02 #{@user_at_localhost} \d.\d+s\n/,
-      "      #{red('WARN')}  All done\n"
+      "      WARN  All done\n"
     )
 
     assert_log_file_lines(
@@ -268,7 +268,8 @@ def test_handles_rake_tasks
   end
 
   def test_log_message_levels
-    configure do |_airbrussh_config, sshkit_config|
+    configure do |airbrussh_config, sshkit_config|
+      airbrussh_config.color = true
       sshkit_config.output_verbosity = Logger::DEBUG
     end
 
@@ -280,9 +281,9 @@ def test_log_message_levels
 
     assert_output_lines(
       "      Test\n",
-      "      #{red('FATAL')} Test\n",
-      "      #{red('ERROR')} Test\n",
-      "      #{yellow('WARN')}  Test\n",
+      "      \e[0;31;49mFATAL\e[0m Test\n",
+      "      \e[0;31;49mERROR\e[0m Test\n",
+      "      \e[0;33;49mWARN\e[0m  Test\n",
       "      Test\n"
     )