use http transport

[tushar00jain]

Summary:
use http transport instead of pg transport -- pg transport fails to resolve address when running locally

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• setup stream dependencies inside work wrapper #248
• only use nightly pytorch in ci #243
• fix compute/communication overlap for gloo #240
• return work from manager allreduce #247
• fix stream dependencies in callbacks #246
• make checkpointing thread safe #245
• -> use http transport #244

[d4l3k]

LGTM