Allow overriding mvn commands

This patch allows the  to over maven
command in order to allow inetgration tests to pass specific
maven flags.

Related to: fabric8io#412

vars/mavenIntegrationTest.groovy

@@ -11,6 +11,8 @@ def call(body) {
  def utils = new Utils()
  def envName = config.environment
  def kubeNS = "-Dfabric8.environment=${envName}"
+ def cmd = cmd ?: "mvn org.apache.maven.plugins:maven-failsafe-plugin:integration-test ${kubeNS} -P openshift-it -Dit.test=${config.itestPattern} -DfailIfNoTests=${config.failIfNoTests} org.apache.maven.plugins:maven-failsafe-plugin:verify"
+
  if (envName) {
  // lets try find the actual kubernetes namespace
  try {
@@ -29,8 +31,7 @@ def call(body) {
  echo "WARNING: Integration tests are current DISABLED for these pipelines!"
 
  } else {
- sh "mvn org.apache.maven.plugins:maven-failsafe-plugin:integration-test ${kubeNS} -P openshift-it -Dit.test=${config.itestPattern} -DfailIfNoTests=${config.failIfNoTests} org.apache.maven.plugins:maven-failsafe-plugin:verify"
-
+ sh cmd
  junitResults(body);
  }
 }