e2e-tests: Add a force option to delete project scenario

Before this change, DeleteProject step only performed project deletion
if there were no open changes within the test project. So, if one of
the test fails, leaving behind an open change. As a result the test
project will not be deleted in the DeleteProject step. Next run of the
same test will also keep failing until the test project is manually
removed.

In a scenario of automotive tests, a CI will keep producing erroneous
test reports, until the user fixes the problem by manually deleting the
test project.

With this change project deletion can be done with force option. Force
deletion is useful because it allows tests to run successively even if
one of the test failed and left an open change in a test project.

To enable forced deletion, an environment property needs to be
configured:
-Dcom.google.gerrit.scenarios.force_project_deletion=true

By default force_project_deletion is set to false.

Change-Id: I2b84419b3665b85465a441a214bf23c420fae0c5

e2e-tests/src/test/resources/data/com/google/gerrit/scenarios/DeleteProject-body.json

@@ -0,0 +1,3 @@
+{
+  "force": "${force_project_deletion}"
+}

e2e-tests/src/test/scala/com/google/gerrit/scenarios/DeleteProject.scala

@@ -20,6 +20,7 @@ import io.gatling.core.structure.ScenarioBuilder
 
 class DeleteProject extends ProjectSimulation {
   private val data: FeederBuilder = jsonFile(resource).convert(keys).queue
+  private val forceKey = "force_project_deletion"
 
   def this(projectName: String) {
     this()
@@ -28,7 +29,10 @@ class DeleteProject extends ProjectSimulation {
 
   val test: ScenarioBuilder = scenario(uniqueName)
       .feed(data)
-      .exec(httpRequest)
+      .exec(session => {
+        session.set(forceKey, getProperty(forceKey, "false"))
+      })
+      .exec(httpRequest.body(ElFileBody(body)).asJson)
 
   setUp(
     test.inject(