Main motivation is move towards a common backend format
for all different types of modes in MinIO, allowing for
a simpler code and predictable behavior across all features.
This PR also brings features such as versioning, replication,
transitioning to single drive setups.
anything that is stuck on the disk today can cause latency
spikes for all incoming S3 I/O, we need to have this
de-coupled so that we can make sure that latency in loading
credentials are not reflected back to the S3 API calls.
The approach this PR takes is by checking if the calls were
updated just in case when the IAM load was in progress,
so that we can use merge instead of "replacement" to avoid
missing state.
- The race happens with a goroutine that refreshes IAM cache data from storage.
- It could lead to deleted users re-appearing as valid live credentials.
- This change also causes CI to run tests without a race flag (in addition to
running it with).
