add ErrataConnector::filter() method

- helper method to implement general filter query pattern
- added workaround for errata endpoint
- support for paginated requests

Works with the following

et.filter('/api/v1/releases', 'filter', is_active="true",
	  enabled="true", name='OpenStack 14.0.z for RHEL 7')

works with the following
et.filter('/errata', 'errata_filter[filter_params]',
	  show_type_RHBA=1, show_type_RHEA=1, show_type_RHSA=1,
	  show_state_NEW_FILES=1, show_state_QE=1,
          show_state_REL_PREP=1,show_state_PUSH_READY=1,
          open_closed_option='exclude', release=856)

Note: errata endpoint releases and products have to be special
handled to include extra [] and multiple entries if you want them

Related: red-hat-storage#132

errata_tool/connector.py

@@ -310,3 +310,30 @@ def get_paginated_data(self, api_url):
             if page_number >= PAGE_LIMIT:
                 raise RuntimeError('hit pagination timeout: %d' % page_number)
         return data
+
+    def filter(self, endpoint, filter_arg, **kwargs):
+        """format and generate filter request
+
+        expose a general filter helper method to format kwargs up
+        as parameters for ET filter request.  Then return generated
+        json object
+        """
+        url = endpoint + "?"
+        param_list = []
+        for k, v in kwargs.items():
+            if k in ('release', 'product'):
+                param_list.append("{0}[{1}][]={2}".format(filter_arg, k, v))
+            else:
+                param_list.append("{0}[{1}]={2}".format(filter_arg, k, v))
+        print(param_list)
+        url = url + "&".join(param_list)
+        if endpoint == '/errata':
+            url = url + '&format=json'
+        print(url)
+
+        if 'paginated' in kwargs and kwargs['paginated']:
+            return {'data': self.get_paginated_data(url)}
+
+        return self._get(url)
+
+