Instana

- Bring back core/util polyfill for Buffer.fromString for backwards compatibility.

- Exponential backoff retry strategy for failed announce attempts. This helps with agents that have not yet attached to the container (and thereby not seen the process) and thus will reject the very first announce attempt.
- Remove polyfill for Buffer.fromString (for Node.js versions up to 4.5 which we no longer support).

- Improve support for pino log calls that only receive a merging object argument.

- Fix Node.js 6 compatibility by downgrading `tar` dependency of `instana/shared-metrics` from `tar6` to `tar5`.

- [Google Cloud Run]: Exclude some revision instance data from compression.

- Improve user experience around native add-on dependencies of `instana/collector`:
- Add precompiled archives for some combination of OS, architecture, libc-flavour and ABI-version.
- Try to use the precompiled native add-on if loading a native add-on fails initially.
- Try to rebuild the native add-on on demand as a fallback.