Vr-server

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* Changed the way blobs are serialized for hashing, now using
JSON to serialize, enabling the test suite to pass on Python 3.
Build and release hashes are likely to be invalidated by moving
to this release. Although the implications aren't well-known,
this change may cause old builds and releases not to match,
which may lead to extra builds and releases.

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* When doing builds, always set LANG=C.UTF-8 to avoid errors
when the builder emits non-ascii.

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* Clean StingRay pool if empty

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* Don't swarm on inactive hosts
* Interpolate env environments mentioned in swarm config

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* Don't try to remove a proc that is not actually running
* Fix procs scooping, to avoid cleaning build artifacts

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* Improve navigation in UI by adding links to various resources
(e.g. procs on host page)