AWS: Added filters to use only completed snaps & ami's and info return to snapshot

[sparshev]

Found that it's actually dangerous to not filter AMI and snapshots by completion - in case snapshot was just taken it will be the first in the list, but still pending so all the requests for the resource uses such snapshot will fail until it will be prepared.

Also added the way to tell the snapshot api user some info about the taken snapshots - just in case he would like to find them later.

Related Issue

fixes: #3

How Has This Been Tested?

Manually

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [x] I have signed the Adobe Open Source CLA.
• [x] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.
• [ ] I have added tests to cover my changes.
• [x] All new and existing tests passed.