bst pull silently failed when there is a network timeout (duplicate of #423)

Summary

If for some reason a remote cache request timeout, the puller print success and buildstream fallback to a local build.

Steps to reproduce

Send a request to a server which never responds.

What is the current bug behavior?

Freezes.

What is the expected correct behavior?

Fail gracefully.

Possible fixes

• Wrap all calls to server in a new function which uses the timeout parameter.
• Raise error with a retry

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