Fix missing rc task (#11)

Description
===========

With the new `Jenkins` file update from #7 we have the option to build `candidate` builds.
The `rc` task requested by the `Jenkinsfile` was missing and this patch implements it.

resolves #8

Changes
=======

![FIX] missing `rc` task for CI system

src/integrationTest/groovy/wooga/gradle/plugins/PluginsPluginIntegrationSpec.groovy

@@ -300,4 +300,18 @@ class PluginsPluginIntegrationSpec extends IntegrationSpec {
         "publishGroovydocs" | _
         "publish"           | _
     }
+
+    @Unroll
+    def "task :#taskAlias will execute :#taskToRun"() {
+        when:
+        def result = runTasks(taskAlias, "--dry-run")
+
+        then:
+        result.standardOutput.contains(":${taskToRun}")
+        !result.standardOutput.contains(":${taskAlias}")
+
+        where:
+        taskAlias | taskToRun
+        "rc"      | "candidate"
+    }
 }

src/main/groovy/wooga/gradle/plugins/PluginsPlugin.groovy

@@ -72,6 +72,7 @@ class PluginsPlugin implements Plugin<Project> {
     private static final String INTEGRATION_TEST_SOURCE = "src/integrationTest/groovy"
     static final String DOC_EXPORT_DIR = "docs/api"
     static final String PUBLISH_GROOVY_DOCS_TASK_NAME = "publishGroovydocs"
+    static final String RC_TASK = "rc"
 
 
     @Override
@@ -88,6 +89,8 @@ class PluginsPlugin implements Plugin<Project> {
             apply(MavenPublishPlugin)
         }
 
+        applyRCtoCandidateAlias(project)
+
         Task integrationTestTask = setupIntegrationTestTask(project, project.tasks)
         Task testTask = project.tasks.getByName(JavaPlugin.TEST_TASK_NAME)
 
@@ -301,4 +304,24 @@ class PluginsPlugin implements Plugin<Project> {
 
         javaConvention.getSourceSets().getByName("integrationTest")
     }
+
+    /**
+     * The {@code NebularRelease} plugin will provide slightly better error messages when using the official
+     * cli tasks (final, candidate, snapshot, ...). Because of internal naming reasons it makes sense for us to use
+     * {@code rc} instead of {@code candidate}. All other resources are named with the
+     * pattern (final, rc and snapshot). I used a custom task with the name {@code rc} which depends on
+     * {@code candidate} but this will fall through the error check in {@code NebularRelease}. So instead we
+     * now change the cli tasklist on the fly. If we find the {@code rc} taskname in the cli tasklist we remove it
+     * and add {@code candidate} instead.
+     * @param project
+     * @return
+     */
+    static void applyRCtoCandidateAlias(Project project) {
+        List<String> cliTasks = project.rootProject.gradle.startParameter.taskNames
+        if (cliTasks.contains(RC_TASK)) {
+            cliTasks.remove(RC_TASK)
+            cliTasks.add(ReleasePlugin.CANDIDATE_TASK_NAME)
+            project.rootProject.gradle.startParameter.setTaskNames(cliTasks)
+        }
+    }
 }