Fixing vagrant build file issues with new vagrant support plugin

Original commit: elastic/x-pack-elasticsearch@dbb5d4a215

qa/vagrant/build.gradle

@@ -1,3 +1,4 @@
+apply plugin: 'elasticsearch.vagrantsupport'
 apply plugin: 'elasticsearch.vagrant'
 
 esvagrant {
@@ -9,4 +10,4 @@ dependencies {
 
     // Inherit Bats test utils from :qa:vagrant project
     bats project(path: ':qa:vagrant', configuration: 'bats')
-}
+}