Closing all idle connections in docker input plugin

[Fiery-Fenix]

This prevents error "too many open files" in most cases

Required for all PRs:

• Updated associated README.md.
• Wrote appropriate unit tests.

resolves #9242

Method Close() of official docker client just closes all idle connections and don't destroy client instance itself:
https://github.com/moby/moby/blob/17.05.x/client/client.go#L181
So it's safe to use inside telegraf input plugin

[telegraf-tiger]

Thanks so much for the pull request!
🤝 ✒️ Just a reminder that the CLA has not yet been signed, and we'll need it before merging. Please sign the CLA when you get a chance, then post a comment here saying !signed-cla

[telegraf-tiger]

Thanks so much for the pull request!
🤝 ✒️ Just a reminder that the CLA has not yet been signed, and we'll need it before merging. Please sign the CLA when you get a chance, then post a comment here saying !signed-cla

[Fiery-Fenix]

!signed-cla

[telegraf-tiger]

Looks like new artifacts were built from this PR. Get them here!

Artifact URLs

• windows_amd64.zip

• windows_i386.zip

• darwin_amd64.tar.gz

• i386.rpm

• freebsd_i386.tar.gz

• linux_i386.tar.gz

• i386.deb

• static_linux_amd64.tar.gz

• linux_mips.tar.gz

• mips.deb

• aarch64.rpm

• linux_arm64.tar.gz

• arm64.deb

• ppc64le.rpm

• linux_ppc64le.tar.gz

• ppc64el.deb

• s390x.rpm

• linux_s390x.tar.gz

• s390x.deb

• linux_mipsel.tar.gz

• mipsel.deb

• armel.rpm

• linux_armel.tar.gz

• armel.deb

• armv6hl.rpm

• freebsd_armv7.tar.gz

• linux_armhf.tar.gz

• armhf.deb

• x86_64.rpm

• freebsd_amd64.tar.gz

• linux_amd64.tar.gz

• amd64.deb

[Fiery-Fenix]

Hey guys, any feedback on this small bug fix?

[akrantz01]

Thanks for the PR! Everything looks good to me.