Add Openstack Swift Recon collector

Add a collector for reporting 'recon' metrics for OpenStack Swift via
the recon cache files. This covers all of the existing recon metrics and
should cover future metrics since it just walks the dict entries.
Include unittests and an empty files fix

Update unittests to include parsing sample *.recon content. It includes an
empty account.recon, a malformed container.recon, and valid object.recon file.
Merge pull request #240 from pandemicsyn/master

Add a Swift Recon Collector