SE-2293 Switch to S3 as the default instance storage type for unit tests

Created by: nizarmah

Switches default storage instance type to S3 and adds Swift storage type override wherever necessary.

JIRA tickets: SE-2293

Dependencies: None

Merge deadline: None

Testing instructions:

1. Use make test in the OCIM virtual machine.

CircleCI build status should be enough.

Reviewers

• @mtyaka