Updating to swift snapshot 2016-05-09-a

[tonystone]

Update vagrant file.

• Moved up to 2016-05-09-a snapshot by default.
• Added apt-get update to update its database.
• Added importing of Swift signature keys.
• Added download of snapshot signature.
• Added validation of snapshot using gpg.
• Added failure path if signature validation does not pass.

  Update process_test_files

• Correct single argument closure requiring parens in latest snapshot.

  Update Geometry.swift

• Changing var to let on matrix.

  Update IntersectionMatrix.swift

• Correcting var description making it internal instead of public.

Ran gyb to update test files for latest swift snapshot changes.

[eswiss]

Looks good. Approved.