build: turn off parallel Verification for premerge/public

Our tests depend on timing (timeouts / sleeps). Therefore we must not overcommit the CPU with highly parallel execution as builds become flaky.

go test can do parallel execution (that's fine as it doesn't overcommit CPU, if only one job is running), but we shouldn't execute different type of
integration tests at the same time.

This commit changes only public (PR + main build) and pre-merge (one build per patch), which are less build time sensitive.

Change-Id: Ib9aaabd301cfa9cd3515a8aa4dd8ae82f58eb811

Jenkinsfile.premerge

@@ -140,8 +140,6 @@ pipeline {
             }
         }
 
-        stage('Verification') {
-            parallel {
                 stage('Cross Compile') {
                     steps {
                         // verify most of the commands, we cannot check everything since some of them
@@ -295,8 +293,6 @@ pipeline {
                         }
                     }
                 }
-            }
-        }
 
         stage('Post') {
             parallel {

Jenkinsfile.public

@@ -121,8 +121,6 @@ pipeline {
             }
         }
 
-        stage('Verification') {
-            parallel {
                 stage('Lint') {
                     steps {
                         sh 'check-mod-tidy'
@@ -357,8 +355,7 @@ pipeline {
                         }
                     }
                 }
-            }
-        }
+
 /*
         stage('UI') {
             when {