Add fixture and test for ES plugin removal

Plugin management code in Elasticsearch should work in union
filesystems as implemented by various Docker Storage Drivers.

Test that the x-pack plugin can be uninstalled correctly as part of
the acceptance tests.

Relates: elastic/elasticsearch#24231

tests/fixtures.py

@@ -25,6 +25,9 @@ def __init__(self):
             self.assert_healthy()
             self.process = Process.get(comm='java')
 
+            # Retain a handle to the Command fixture letting us execute commands within the container(s)
+            self.command = Command
+
             # Start each test with a clean slate.
             assert self.load_index_template().status_code == codes.ok
             assert self.delete().status_code == codes.ok
@@ -112,4 +115,15 @@ def assert_healthy(self):
                 assert self.get_node_count() == 2
                 assert self.get_cluster_status() == 'green'
 
+        def uninstall_plugin(self, plugin_name):
+            # This will run on only one host, but this is ok for the moment
+            # TODO: as per http://testinfra.readthedocs.io/en/latest/examples.html#test-docker-images
+            uninstall_output = self.command.run(' '.join(["bin/elasticsearch-plugin",
+                                                          "-s",
+                                                          "remove",
+                                                          "{}".format(plugin_name)]))
+            # Reset elasticsearch to its original state
+            self.reset()
+            return uninstall_output
+
     return Elasticsearch()

tests/test_es_plugins.py

@@ -0,0 +1,7 @@
+from .fixtures import elasticsearch
+from requests import codes
+
+
+def test_uninstall_xpack_plugin(elasticsearch):
+    # Ensure plugins can be uninstalled, see https://github.com/elastic/elasticsearch/issues/24231
+    assert elasticsearch.uninstall_plugin("x-pack").exit_status == 0