Backend.ai

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- Add metadata/aliases for TensorFlow v1.5 kernel images to the default sample configs.
- Polish CI and test suites.
- Add etcd put/get/del manager CLI commands to get rid of the necessity of an extra
etcdcli binary during installation. (lablup/backend.ai15)

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- Minor update to fix dependency versions.

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NOTICE
- From this release, the manager and agent versions will go together, which indicates
the compatibility of them, even when either one has relatively little improvements.
CHANGES
- Include the exit code of the last executed in-kernel process when returning
`build-finished` or `finished` results in the batch mode.
- Improve logging to support rotating file-based logs.
- Upgrade aiotools to v0.5.2 release.
- Remove the image name prefix when reporting available images. (51)
- Improve debug-kernel mode to mount host-side kernel runner source into the kernel
containers so that they use the latest, editable source clone of the kernel runner.

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* Change StreamPty methods to become coroutines to match with aiohttp v3
API changes.

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* Fix file upload handling in the asyncio version.
* Stringifying exception classes now use the output of "repr()".

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* Improve asyncio exception handling.
Now it does NOT silently swallow CancelledError/TimeoutError and other
non-aiohttp errors!