add a one-line summary to the package metadata
add a one-line summary to the package metadata

This summary is used on PyPI and when building release announcement
emails.

Change-Id: I778d7efa5415c8b499d6994ed4108d2b3a2faee7
Signed-off-by: Doug Hellmann <0798ebecfb7bc4dfb9d0445c2fa030eb64e1fa1c@doughellmann.com>

stackforge/monasca-notification,openstack/monasca-notification,openstack/monasca-notification,sapcc/monasca-notification