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: I1367bf31b01280cd675da6c6f93125f029183e06
Signed-off-by: Doug Hellmann <0798ebecfb7bc4dfb9d0445c2fa030eb64e1fa1c@doughellmann.com>

sapcc/monasca-agent,sapcc/monasca-agent,sapcc/monasca-agent