incorrect string format for app loading debug message

[Lin Yang]

When launch murano-api, the parameters {app_name} and {conf_file} in the debug message printed by app_loader didn't be replaced by meaningful value as expected.

https://github.com/openstack/murano/blob/master/murano/common/app_loader.py#L82-L83

Current debug info:

2015-08-05 04:26:55.652 7273 DEBUG murano.common.app_loader [-] Loading %(app_name)s from %(conf_file)s load_paste_app /opt/stack/murano/murano/common/app_loader.py:83

Expected debug info:

2015-08-05 04:36:48.431 11118 DEBUG murano.common.app_loader [-] Loading murano from /etc/murano/murano-paste.ini load_paste_app /opt/stack/murano/murano/common/app_loader.py:83

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/209339

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/209339
Committed: https://git.openstack.org/cgit/openstack/murano/commit/?id=1c468d99b36b46efb535092581f8f6ad091f6586
Submitter: Jenkins
Branch: master

commit 1c468d99b36b46efb535092581f8f6ad091f6586
Author: Lin Yang <email address hidden>
Date: Wed Aug 5 12:47:08 2015 +0800

    Fix incorrect format syntax in app_loader

    The syntax %()s is incorrect in string.format(). Changed it to {}.

    Change-Id: I2ff0c8b4ee05f7dd854bffbfa25417a20c494fff
    Closes-Bug: #1481578