feat: Enable chrony and host-based time sync by default on Ubuntu 18.04

[ericsuhong]

Reason for Change:
Use chrony + host-based time sync which is a recommended way and also work in airgap clouds.

All Azure Ubuntu 18.04 stock images already come with chrony enabled as well.

Issue Fixed:
#2552

Credit Where Due:

Does this change contain code from or inspired by another project?

• No
• Yes

If "Yes," did you notify that project's maintainers and provide attribution?

• No
• Yes

Requirements:

• uses conventional commit messages
• includes documentation
• adds unit tests
• tested upgrade from previous version

Notes:
Reference: https://docs.microsoft.com/en-us/azure/virtual-machines/linux/time-sync

[jackfrancis]

/azp run pr-e2e

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[jackfrancis]

/azp run pr-e2e

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[codecov]

Codecov Report

Merging #4011 (e70b683) into master (5dbff4c) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #4011   +/-   ##
=======================================
  Coverage   73.08%   73.08%           
=======================================
  Files         145      145           
  Lines       21776    21776           
=======================================
  Hits        15914    15914           
  Misses       4829     4829           
  Partials     1033     1033           

Impacted Files	Coverage Δ
pkg/engine/templates_generated.go	43.70% <ø> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 5dbff4c...e70b683. Read the comment docs.

[ericsuhong]

/azp run pr-e2e

[azure-pipelines]

Commenter does not have sufficient privileges for PR 4011 in repo Azure/aks-engine

[jackfrancis]

In order for this to work on 18.04 prior to building a new VHD w/ chrony already installed is to protect the configureChrony and ensureChrony invokations inside a if apt list --installed | grep 'chrony'; then block.

Otherwise we're going to get a CSE error on all 18.04 VHD nodes ("distro": "aks-ubuntu-18.04"):

+ sleep 5
+ for i in $(seq 1 $retries)
+ timeout 30 systemctl daemon-reload
+ timeout 30 systemctl restart chrony
Failed to restart chrony.service: Unit chrony.service not found.
+ '[' 100 -eq 100 ']'
+ return 1
+ ret=1
+ systemctl status chrony --no-pager -l
Unit chrony.service could not be found.
+ '[' 1 -ne 0 ']'
+ return 1
+ exit 4

[jackfrancis]

tested this changeset locally using the non-VHD 18.04 image and am consistently getting a failure in this E2E scenario:

https://github.com/Azure/aks-engine/blob/master/test/e2e/kubernetes/kubernetes_test.go#L2724

(not sure why, will have to look into it)

[jackfrancis]

cc @Michael-Sinz @jadarsie

This passes my smoke tests, am planning to merge.

[jackfrancis]

/azp run pr-e2e

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[jackfrancis]

/lgtm

[acs-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ericsuhong, jackfrancis

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [jackfrancis]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment