OpenCensue: GAUGE_DISTRIBUTION metric not exported

[imccarten1]

Describe the bug
I was trying to use a custom receiver module to export some metrics converted from the opencensus-proto format with internaldata.OCSliceToMetrics. I discovered that it does not export metrics of type MetricDescriptor_GAUGE_DISTRIBUTION.

Steps to reproduce
Create a metric in opencensus-proto format of type MetricDescriptor_GAUGE_DISTRIBUTION and try to convert it using internaldata.OCSliceToMetrics.
Once the pull request to update https:/GoogleCloudPlatform/appengine-sidecars-docker/tree/master/opentelemetry_collector to use opentelemetry-collector v 0.14.0 has been approved it should be possible to reproduce this issue with the vm image age receiver in that repository.

What did you expect to see?
A clear and concise description of what you expected to see.
I expected the GAUGE_DISTRIBUTION metric to exported.

What did you see instead?
A clear and concise description of what you saw instead.
The metric was silently dropped. It wasn't exported without anything in the logs indicating an error.

What version did you use?
Version: (e.g., v0.4.0, 1eb551b, etc)
0.14.0

What config did you use?
Config: (e.g. the yaml config file)
Note that this includes reference to a custom receiver defined at https:/GoogleCloudPlatform/appengine-sidecars-docker/tree/master/opentelemetry_collector

receivers:
vmimageage:
build_date: 2020-11-04T01:01:28+00:00
vm_image_name: example_image
export_interval: 10s

processors:
resource:
type: gae_instance
labels: {
"cloud.region": "australia-southeast1",
"appengine.service.id": "default",
"appengine.version.id": "test-version",
"appengine.instance.id": "test-instance",
}

exporters:
stackdriver:
project: test-project
metric:
prefix: appengine.googleapis.com/flex/internal
skip_create_descriptor: true

service:
pipelines:
metrics:
receivers: [vmimageage]
processors: [resource]
exporters: [stackdriver]

Environment
OS: (e.g., "Ubuntu 20.04") Debian GNU/Linux rodete
Compiler(if manually compiled): (e.g., "go 14.2") go1.15 linux/amd64

Additional context
Add any other context about the problem here.

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