Fix creation of resources in _detector

[xrmx]

We should create a Resource instance and not use Resource.create because if we set OTEL_EXPERIMENTAL_RESOURCE_DETECTORS we will go into an infinite loop trying to load and instantiate all the resources detectors.

See Resource.create implementation

Fix #363

[aabmass]

We have discourage using the constructor. If we only call the constructor, there is no way to get these attributes https://github.com/open-telemetry/opentelemetry-python/blob/b48223561acfdffd1411ed7d015ddabe6f6eb801/opentelemetry-sdk/src/opentelemetry/sdk/resources/__init__.py#L217-L227 or OTEL_RESOURCE_ATTRIBUTES based ones.

I think we might need to fix it this in the SDK or at least update the documentation to say that detectors MUST call the constructor. It seems a bit fragile overall, wdyt?

[aabmass]

/gcbrun

[xrmx]

We have discourage using the constructor. If we only call the constructor, there is no way to get these attributes https://github.com/open-telemetry/opentelemetry-python/blob/b48223561acfdffd1411ed7d015ddabe6f6eb801/opentelemetry-sdk/src/opentelemetry/sdk/resources/__init__.py#L217-L227 or OTEL_RESOURCE_ATTRIBUTES based ones.

I think we might need to fix it this in the SDK or at least update the documentation to say that detectors MUST call the constructor. It seems a bit fragile overall, wdyt?

Opened a pr to update the docs

[aabmass]

/gcbrun

[aabmass]

@xrmx to fix the tests, can you regenerate the snapshots by running? That will highlight the difference in behavior too

tox -f py3xx-test -- --snapshot-update

[xrmx]

@xrmx to fix the tests, can you regenerate the snapshots by running? That will highlight the difference in behavior too

tox -f py3xx-test -- --snapshot-update

Updated the snapshosts, thanks for the hint

[aabmass]

/gcbrun