Support EXPLAIN on Greenplum. Fixes #3097

- Extract SQLEditor.execute and SQLEditor._poll into their own files and add test around them
 - Extract SQLEditor backend functions that start executing query to their own files and add tests around it
 - Move the Explain SQL from the front-end and now pass the Explain plan parameters as a JSON object in the start query call.
 - Extract the compile_template_name into a function that can be used by the different places that try to select the version of the template and the server type

web/pgadmin/utils/compile_template_name.py

@@ -0,0 +1,17 @@
+##########################################################################
+#
+# pgAdmin 4 - PostgreSQL Tools
+#
+# Copyright (C) 2013 - 2018, The pgAdmin Development Team
+# This software is released under the PostgreSQL Licence
+#
+##########################################################################
+import os
+
+
+def compile_template_name(template_prefix, template_file_name, server_type, version):
+    if server_type == 'gpdb':
+        version_path = '#{0}#{1}#'.format(server_type, version)
+    else:
+        version_path = '#{0}#'.format(version)
+    return os.path.join(template_prefix, version_path, template_file_name)

web/pgadmin/utils/tests/test_compile_template_name.py

@@ -0,0 +1,34 @@
+#######################################################################
+#
+# pgAdmin 4 - PostgreSQL Tools
+#
+# Copyright (C) 2013 - 2018, The pgAdmin Development Team
+# This software is released under the PostgreSQL Licence
+#
+##########################################################################
+from pgadmin.utils.compile_template_name import compile_template_name
+from pgadmin.utils.route import BaseTestGenerator
+
+
+class StartRunningQueryTest(BaseTestGenerator):
+    """
+    Check that the apply_explain_plan_weapper_if_needed method works as intended
+    """
+    scenarios = [
+        ('When server is Postgres and version is 10, it returns the path to the postgres template', dict(
+            server_type='pg',
+            version=100000,
+
+            expected_return_value='some/prefix/#100000#/some_file.sql'
+        )),
+        ('When server is GreenPlum and version is 5, it returns the path to the GreenPlum template', dict(
+            server_type='gpdb',
+            version=80323,
+
+            expected_return_value='some/prefix/#gpdb#80323#/some_file.sql'
+        )),
+    ]
+
+    def runTest(self):
+        result = compile_template_name('some/prefix', 'some_file.sql', self.server_type, self.version)
+        self.assertEquals(result, self.expected_return_value)

web/pgadmin/utils/versioned_template_loader.py

@@ -6,7 +6,6 @@
 # This software is released under the PostgreSQL Licence
 #
 ##########################################################################
-
 from flask.templating import DispatchingJinjaLoader
 from jinja2 import TemplateNotFound
 
@@ -54,6 +53,7 @@ class VersionedTemplateLoader(DispatchingJinjaLoader):
 
             template_path = path_start + '/' + \
                 server_version['name'] + '/' + file_name
+
             try:
                 return super(VersionedTemplateLoader, self).get_source(
                     environment, template_path