Added EXECUTOR_COUNT to environment variables

jenkinsci/workflow-durable-task-step-plugin#106

Signed-off-by: Artur Harasimiuk <artur.harasimiuk@intel.com>

Author: ArturHarasimiuk

core/src/main/java/jenkins/model/CoreEnvironmentContributor.java

@@ -65,6 +65,7 @@ public void buildEnvironmentFor(Job j, EnvVars env, TaskListener listener) throw
             Node n = e.getOwner().getNode();
             if (n != null)
                 env.put("NODE_LABELS", Util.join(n.getAssignedLabels(), " "));
+            env.put("EXECUTOR_COUNT", String.valueOf(e.getOwner().countExecutors()));
         }
     }
 }

core/src/main/resources/jenkins/model/CoreEnvironmentContributor/buildEnv.groovy

@@ -3,7 +3,7 @@ package jenkins.model.CoreEnvironmentContributor;
 def l = namespace(lib.JenkinsTagLib)
 
 // also advertises those contributed by Run.getCharacteristicEnvVars()
-["BUILD_NUMBER","BUILD_ID","BUILD_DISPLAY_NAME","JOB_NAME", "JOB_BASE_NAME","BUILD_TAG","EXECUTOR_NUMBER","NODE_NAME","NODE_LABELS","WORKSPACE","JENKINS_HOME","JENKINS_URL","BUILD_URL","JOB_URL"].each { name ->
+["BUILD_NUMBER","BUILD_ID","BUILD_DISPLAY_NAME","JOB_NAME", "JOB_BASE_NAME","BUILD_TAG","EXECUTOR_COUNT","EXECUTOR_NUMBER","NODE_NAME","NODE_LABELS","WORKSPACE","JENKINS_HOME","JENKINS_URL","BUILD_URL","JOB_URL"].each { name ->
     l.buildEnvVar(name:name) {
         raw(_("${name}.blurb"))
     }

core/src/main/resources/jenkins/model/CoreEnvironmentContributor/buildEnv.properties

@@ -4,6 +4,7 @@ BUILD_DISPLAY_NAME.blurb=The display name of the current build, which is somethi
 JOB_NAME.blurb=Name of the project of this build, such as "foo" or "foo/bar".
 JOB_BASE_NAME.blurb=Short Name of the project of this build stripping off folder paths, such as "foo" for "bar/foo".
 BUILD_TAG.blurb=String of "jenkins-<i>$'{'JOB_NAME}</i>-<i>$'{'BUILD_NUMBER}</i>". All forward slashes ("/") in the JOB_NAME are replaced with dashes ("-"). Convenient to put into a resource file, a jar file, etc for easier identification.
+EXECUTOR_COUNT.blurb=Number of executors available on currently running node
 EXECUTOR_NUMBER.blurb=\
   The unique number that identifies the current executor \
   (among executors of the same machine) that\u2019s \