Handle errors raised by plugins more gracefully in mod_wsgi.

This started as an effort to display a more useful error message in the
Apache error log if retrieving the schema failed. I broadened the scope
a little to include limiting the output in the Apache error log
so errors are easier to find.

This adds a new configuration option, startup_traceback. Outside of
lite-server.py it is False by default so does not display the traceback
that lead to the StandardError being raised. This makes the mod_wsgi
error much easier to follow.

ipalib/plugins/migration.py

@@ -31,7 +31,10 @@ from ipalib import api, errors, output, uuid
 from ipalib import Command, List, Password, Str
 from ipalib.cli import to_cli
 if api.env.in_server and api.env.context in ['lite', 'server']:
-    from ipaserver.plugins.ldap2 import ldap2
+    try:
+        from ipaserver.plugins.ldap2 import ldap2
+    except StandardError, e:
+        raise e
 from ipalib import _
 from ipalib.text import Gettext # FIXME: remove once the other Gettext FIXME is removed