db: Add retry on initial connect

Creating the metadata is the very first action on startup and can fail
if the database is not (yet) available. Add our eponymous retry logic
there as well.

Also, increase the backoff base to a whopping two seconds because
database startup/restart is just a very slow operation.

Closes: scVENUS#177.

peekaboo/db.py

@@ -161,9 +161,25 @@ def __init__(self, db_url, instance_id=0,
         # attempt 3: 10 * 2**(3) == 40-80msecs
         # attempt 4: 10 * 2**(4) == 80-160msecs
         self.deadlock_backoff_base = 10
-        self.connect_backoff_base = 100
+        self.connect_backoff_base = 2000
 
-        Base.metadata.create_all(self.__engine)
+        with self.__lock:
+            attempt = 1
+            while attempt <= self.retries:
+                try:
+                    Base.metadata.create_all(self.__engine)
+                except (OperationalError, DBAPIError,
+                        SQLAlchemyError) as error:
+                    attempt = self.was_transient_error(
+                        error, attempt, 'create metadata')
+                    if attempt > 0:
+                        continue
+
+                    raise PeekabooDatabaseError(
+                        'Failed to create schema in database: %s' %
+                        error)
+
+                break
 
     def was_transient_error(self, error, attempt, action):
         """ Decide if an exception signals a transient error condition and