[test] add lang-expression plugin to vagrant tests

we need this now that #13726 has been merged

qa/vagrant/pom.xml

@@ -171,6 +171,12 @@
                                     <version>${elasticsearch.version}</version>
                                     <type>zip</type>
                                 </artifactItem>
+                                <artifactItem>
+                                    <groupId>org.elasticsearch.plugin</groupId>
+                                    <artifactId>lang-expression</artifactId>
+                                    <version>${elasticsearch.version}</version>
+                                    <type>zip</type>
+                                </artifactItem>
                                 <artifactItem>
                                     <groupId>org.elasticsearch.plugin</groupId>
                                     <artifactId>lang-javascript</artifactId>

qa/vagrant/src/test/resources/packaging/scripts/plugin_test_cases.bash

@@ -191,6 +191,10 @@ fi
     install_and_check_plugin discovery multicast
 }
 
+@test "[$GROUP] install lang-expression plugin" {
+    install_and_check_plugin lang expression
+}
+
 @test "[$GROUP] install javascript plugin" {
     install_and_check_plugin lang javascript rhino-*.jar
 }
@@ -287,6 +291,10 @@ fi
     remove_plugin discovery-multicast
 }
 
+@test "[$GROUP] remove lang-expression plugin" {
+    remove_plugin lang-expression
+}
+
 @test "[$GROUP] remove javascript plugin" {
     remove_plugin lang-javascript
 }