Fixing VMM & RNG per-device metrics. (Minor Tap fix)

[bstrong04]

Changes

Added a new device metric system for both RNG and VMM VIRTIO devices. This includes mapping them through a BTreeMap as mentioned in issue #4145 for the net devices. Handles multiple devices through ID matching while also adding an Arc to each metric to make them thread safe. Also adds some minor tests replicating the ones in the net devices folder to check for thread safety and aggregation functionality.

Also resolves all former references to metrics within the vsock and rng objects to a reference to the "global" id set to arbitrarily point to the single required vsock and rng devices for their respective files.

Also adds a minor fix to the test_tap_name method allowing for regex matching.

Reason

Done to allow unit tests to run in parallel to each other. In production one vsock device and one rng device suffice for use, but with this implementation device metrics will overwrite each other during testing and tests would have to be run sequentially. Therefore, support for a global metric and multiple other metrics during testing is needed to ensure functionality for tests and production. This behavior is simply replicated on both vsock and rng.

test_tap_name changed from prior hardcoded value of tap0 to handle any numerical value after 'tap' when passed in.

Closes #4709

Worked with @gjkeller for this.

License Acceptance

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• [ ] This functionality cannot be added in rust-vmm.