[QOLDEV-915] fix integration with QA plugin

- Previously we detected the QA plugin presence by checking for it in the config, but this has stopped working,
possibly as part of the CKAN 2.10 upgrade. Change it to instead attempt the necessary imports and rely on that.

NB This will cause ckanext-data-qld to implement the IQA interface if QA is installed but not enabled.
However, that should not be problematic, since the interface will simply do nothing if QA is not running.

ckanext/data_qld/plugin.py

@@ -19,11 +19,14 @@
 from .resource_freshness import validation as resource_freshness_validator
 from .resource_freshness.logic.actions import get as resource_freshness_get_actions
 
-if ' qa' in tk.config.get('ckan.plugins', ''):
+try:
     from ckanext.qa.interfaces import IQA
     import ckanext.qa.lib as qa_lib
     import ckanext.qa.tasks as qa_tasks
     import os
+    qa_present = True
+except ImportError:
+    qa_present = False
 
 
 log = logging.getLogger(__name__)
@@ -43,7 +46,7 @@ class DataQldPlugin(plugins.SingletonPlugin):
     plugins.implements(plugins.IBlueprint)
     plugins.implements(plugins.IClick)
 
-    if ' qa' in tk.config.get('ckan.plugins', ''):
+    if qa_present:
         plugins.implements(IQA)
 
     # IConfigurer