[CI][v1.6.x] Fix blocked pipelines [windows,unix-cpu,unix-gpu] on v1.6.x

[ChaiBapchya]

Fixes following issues in the following pipelines

Fix setRefClass not found issue by adding import of library methods
Fixes #17920
[unix-cpu] - R: CPU
[unix-cpu] - R: MKLDNN-CPU
[unix-gpu] - R: GPU
[website] - R Docs

[website] - Jekyll website
rvm version error [fix by pinning the updated version 2.6.3]

[unix-cpu] - Tests / Python3: MKLDNN-MKL-CPU
test_quantize flaky test
Fix : cherrypick the commit from master that fixed this flakiness issue

[unix-gpu] - Static build GPU 14.04 Python
gnu_tls handshake failed [NVIDIA Docker no longer supported on Ubuntu 14.04 hence TLS / certificate issue upon apt-get update]
Fix : switch from https to http

[mxnet-bot]

Hey @ChaiBapchya , Thanks for submitting the PR
All tests are already queued to run once. If tests fail, you can trigger one or more tests again with the following commands:

• To trigger all jobs: @mxnet-bot run ci [all]
• To trigger specific jobs: @mxnet-bot run ci [job1, job2]

---

CI supported jobs: [centos-gpu, unix-gpu, website, centos-cpu, sanity, windows-cpu, windows-gpu, unix-cpu, miscellaneous, edge, clang]

---

Note:
Only following 3 categories can trigger CI :PR Author, MXNet Committer, Jenkins Admin.
All CI tests must pass before the PR can be merged.

[ChaiBapchya]

@mxnet-bot run ci [unix-cpu]

[ChaiBapchya]

Testing this locally, able to reproduce the docs error

Loading mxnet
[1] "Loading local: inst/libs/libmxnet.so"
<simpleError in find.package(package, lib.loc, verbose = verbose): there is no package called 'mxnet'
>
[1] "Loading local: src/mxnet.so"
<simpleError in find.package(package, lib.loc, verbose = verbose): there is no package called 'mxnet'
>
Error in loadModule("mxnet", TRUE) : could not find function "loadModule"
Calls: <Anonymous> ... load_code -> <Anonymous> -> run_pkg_hook -> <Anonymous>
Execution halted

However, upon checking the local files, both mxnet.so and libmxnet.so exist.
So dyn.load isn't able to find package

> ls R-package/inst/libs/
libmxnet.so

> ls R-package/src/
libmxnet.so

[ChaiBapchya]

Cherrypicking Python2 -> Python3 related PRs I found after doing a git diff between v1.6.x branch and master
v1.6.x...ChaiBapchya:master

[ChaiBapchya]

@mxnet-bot run ci [unix-gpu]

[mxnet-bot]

Jenkins CI successfully triggered : [unix-gpu]

[ChaiBapchya]

So as it turns out, it wasn't needed to cherrypick previous PRs.
Because even without migrating CI from Py2 to Py3 docs test pass
@aaronmarkham @leezu @aaronmarkham
Plz review/merge. Thanks.

[ChaiBapchya]

@lanking520 @zachgk any idea about the Scala failure? http://jenkins.mxnet-ci.amazon-ml.com/blue/organizations/jenkins/mxnet-validation%2Funix-cpu/detail/PR-17993/4/pipeline

Since this is a network issue, generally gets resolved by retriggering the build.

Looking into the Static build 14.04 Python unix-gpu failure : it fails at apt-get update in ubuntu_publish.sh
it is on ubuntu 14.04 with nvidia-docker.
Surprisingly, master branch doesn't fail. Nor do previous commits in 1.6 branch.

[ChaiBapchya]

@mxnet-bot run ci [unix-cpu]

[mxnet-bot]

Jenkins CI successfully triggered : [unix-cpu]

[ChaiBapchya]

Fixes #18005

[ChaiBapchya]

It's weird why 1.6 branch is facing rvm version error.
All the previous 5 builds had passed for Jekyll build.

[ChaiBapchya]

@mxnet-bot run ci [unix-cpu]

[mxnet-bot]

Jenkins CI successfully triggered : [unix-cpu]

[zixuanweeei]

Just a reminder: #11747 (comment)

[ChaiBapchya]

@mxnet-label-bot add [pr-awaiting-review]

[ChaiBapchya]

@sandeep-krishnamurthy @zixuanweeei @leezu @aaronmarkham Pl help review.