[bug] handle MissingDesignDocError after get_sync_info

MissingDesignDocError raised on get_sync_info due to a missing design
document will be handled by the server during sync.
Ensure is now False by default, and thus database creation can deliver
an empty one that will be ensured during sync, following the ensure
parameter.

client/changes/bug_missing_design_doc_handler

+o Handle missing design doc at GET (get_sync_info). Soledad server can handle this during sync.

client/src/leap/soledad/client/sync.py

@@ -22,6 +22,7 @@ import logging
 from twisted.internet import defer
 
 from u1db import errors
+from leap.soledad.common.errors import MissingDesignDocError
 from u1db.sync import Synchronizer
 
 
@@ -73,8 +74,9 @@ class SoledadSynchronizer(Synchronizer):
             (self.target_replica_uid, target_gen, target_trans_id,
              target_my_gen, target_my_trans_id) = yield \
                 sync_target.get_sync_info(self.source._replica_uid)
-        except errors.DatabaseDoesNotExist:
+        except (errors.DatabaseDoesNotExist, MissingDesignDocError) as e:
             logger.debug("Database isn't ready on server. Will be created.")
+            logger.debug("Reason: %s", e.__class__)
             self.target_replica_uid = None
             target_gen, target_trans_id = 0, ''
             target_my_gen, target_my_trans_id = 0, ''