remove machine id in ubuntu images

[Sunnatillo]

Copy of #675, #675 could not be tested due to CI constraints.
Authored by @jklippel

"Currently the image contains an id in /etc/machine-id. This file should contain a unique machine ID which uniquely identifies the host (see machine-id(5)).
Some processes rely on this file to generate other values e.g. mac-addresses on bond interfaces.
If the machine-id is the same accross many hosts
these mac-addresses will under certain circumstances be generated identically. Two hosts having the same mac address leads to L2-networking issues.

This commit empties the machine-id file so that it is regenerated on the next boot (which will be the first boot of the machine the image is used for)."

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[Sunnatillo]

/test-integration-metal3-dev-tools-centos
/test-integration-metal3-dev-tools-ubuntu

[Sunnatillo]

/test-integration-metal3-dev-tools-ubuntu

[Sunnatillo]

/test-integration-metal3-dev-tools-ubuntu

[Sunnatillo]

/test-integration-metal3-dev-tools-centos
/test-integration-metal3-dev-tools-ubuntu

[mquhuy]

/test-integration-metal3-dev-tools-ubuntu

[metal3-io-bot]

@Sunnatillo: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
markdownlint	3f3d4d7	link	true	/test markdownlint

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[metal3-io-bot]

PR needs rebase.

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