fix(test): remove broken monitor action for Cucumber

The issue is that it resulted in the following sequence of actions:
- run karma start
- run karma run
- and then instantly kill karma start command

This resulted in flaky tests because preliminary killing resulted in
incomplete output. In fact test was unnecessary complicated as it was
enough to use runOut, which asserts output of the karma run command.

test/e2e/error.feature

@@ -18,7 +18,7 @@ Feature: Error Display
       """
       SyntaxError: Unexpected token }
       """
-  Scenario: Single-run Syntax Error in a test file
+  Scenario: Not single-run Syntax Error in a test file
     Given a configuration with:
       """
       files = ['error/test.js', 'error/under-test.js'];
@@ -29,8 +29,7 @@ Feature: Error Display
       ];
       singleRun = false;
       """
-    When I monitor Karma
-    And I stop when the log contains 'SyntaxError'
+    When I runOut Karma
     Then it fails with like:
       """
       SyntaxError: Unexpected token }

test/e2e/step_definitions/core_steps.js

@@ -64,7 +64,7 @@ cucumber.defineSupportCode((a) => {
         }
 
         const runOut = command === 'runOut'
-        if (command === 'run' || command === 'runOut' || command === 'monitor') {
+        if (command === 'run' || command === 'runOut') {
           this.child = spawn('' + runtimePath, ['start', '--log-level', 'warn', configFile])
           const done = () => {
             cleansingNeeded = true
@@ -87,18 +87,16 @@ cucumber.defineSupportCode((a) => {
             setTimeout(() => {
               exec(cmd, {
                 cwd: baseDir
-              }, (error, stdout) => {
+              }, (error, stdout, stderr) => {
                 if (error) {
                   this.lastRun.error = error
                 }
                 if (runOut) {
                   this.lastRun.stdout = stdout
+                  this.lastRun.stderr = stderr
                 }
                 done()
               })
-              if (command === 'monitor') {
-                done()
-              }
             }, 1000)
           })
         } else {
@@ -180,15 +178,6 @@ cucumber.defineSupportCode((a) => {
     execKarma.apply(this, [command, undefined, proxyPort, proxyPath, callback])
   })
 
-  When('I stop when the log contains {string}', function (message, callback) {
-    setInterval(() => {
-      if (this.lastRun.stdout.includes(message)) {
-        this.child && this.child.kill()
-        callback()
-      }
-    }, 100)
-  })
-
   defineParameterType({
     name: 'exact',
     regexp: /no\sdebug|like/