Rework the default handlers into layer-openstack-*

Due to commit 95493a4 in charms.reactive, the default handlers in
charms.openstack broke.  This is because charms.reactive no longer will
run handlers that are not in the hooks/ or reactive/ directory tree; the
default handlers in charms.openstack are in the library code, which is
pip installed into the module packages.

This patch, and related patches in charms.openstack and layer-openstack
enable the default handlers to function again.  Note that from a charm
author perspective, the API to default handlers is identical.  This is
merely an implementation change.

Change-Id: I38d46eaab3d64dd43166957a4aee01163bc00f5b
Partial-Bug: #1707685

reactive/layer_openstack_api.py

@@ -0,0 +1,64 @@
+# attempt to move the default status handler here:
+import charmhelpers.core.hookenv as hookenv
+
+import charms_openstack.charm as charm
+import charms.reactive as reactive
+
+
+@reactive.when('amqp.connected',
+               'charms.openstack.do-default-amqp.connected')
+def default_amqp_connection(amqp):
+    """Handle the default amqp connection.
+
+    This requires that the charm implements get_amqp_credentials() to
+    provide a tuple of the (user, vhost) for the amqp server
+    """
+    with charm.provide_charm_instance() as instance:
+        user, vhost = instance.get_amqp_credentials()
+        amqp.request_access(username=user, vhost=vhost)
+        instance.assess_status()
+
+
+@reactive.when('shared-db.connected',
+               'charms.openstack.do-default-shared-db.connected')
+def default_setup_database(database):
+    """Handle the default database connection setup
+
+    This requires that the charm implements get_database_setup() to provide
+    a list of dictionaries;
+    [{'database': ..., 'username': ..., 'hostname': ..., 'prefix': ...}]
+
+    The prefix can be missing: it defaults to None.
+    """
+    with charm.provide_charm_instance() as instance:
+        for db in instance.get_database_setup():
+            database.configure(**db)
+        instance.assess_status()
+
+
+@reactive.when('identity-service.connected',
+               'charms.openstack.do-default-identity-service.connected')
+def default_setup_endpoint_connection(keystone):
+    """When the keystone interface connects, register this unit into the
+    catalog.  This is the default handler, and calls on the charm class to
+    provide the endpoint information.  If multiple endpoints are needed,
+    then a custom endpoint handler will be needed.
+    """
+    with charm.provide_charm_instance() as instance:
+        keystone.register_endpoints(instance.service_type,
+                                    instance.region,
+                                    instance.public_url,
+                                    instance.internal_url,
+                                    instance.admin_url)
+        instance.assess_status()
+
+
+@reactive.when('identity-service.available',
+               'charms.openstack.do-default-identity-service.available')
+def default_setup_endpoint_available(keystone):
+    """When the identity-service interface is available, this default
+    handler switches on the SSL support.
+    """
+    with charm.provide_charm_instance() as instance:
+        instance.configure_ssl(keystone)
+        instance.assess_status()