EUCA_7737
initial implmentation of shared public data set for all and amazon images
EUCA-7737
added support for regions, so that each public data set is fetched for each region
Merge branch 'testing' into EUCA-7737
Add missing import; minor PEP8 cleanup
Merge pull request #134 from eucalyptus/EUCA-7737

Euca 7737