Reconfigure cloud-init to use ec2-user instead of centos on Amazon Linux

[sfzylad]

What this PR does / why we need it:

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #536

Special notes for your reviewer:

Please confirm that if this PR changes any image versions, then that's the sole change this PR makes.

Release note:

[k8s-ci-robot]

Hi @sfzylad. Thanks for your PR.

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[sfzylad]

With this changes I was able to bake an AMI and login as ec2-user. User centos is no longer present.

[randomvariable]

Does this get overwritten by package upgrades by any chance?

[randomvariable]

i.e. is this marked properly as a config file in the RPM?

[sfzylad]

The file belongs to the RPM and is marked as a config file:

[root@ip-10-0-1-54 ~]# rpm -qf /etc/cloud/cloud.cfg
cloud-init-18.3+52.gc5f78957-1.el7.noarch
[root@ip-10-0-1-54 ~]# rpm -qc cloud-init-18.3+52.gc5f78957-1.el7.noarch |grep cloud.cfg
/etc/cloud/cloud.cfg

[randomvariable]

/ok-to-test

[detiber]

/approve

@randomvariable or @chuckha want to give final lgtm?

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: detiber, sfzylad

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[chuckha]

Do we need all of these modules (and config_modules and final_modules)? Like salt-minion.

[detiber]

In this case I think this is fine, since this file is directly from the cloud-init package and tweaked for the correct default user.

[chuckha]

/lgtm

In summary, this takes the standard config file out of the package that we were already installing and customizes it slightly so that it works on amazon-linux.

The file is marked as a config file so upgrades will not overwrite the customization.