fix: adding additional device for package iso and disk size as a string

[bugbuilder]

Description

sles-15.json and sles-15-sp1.json builders needs an additional package iso to accomplish a new images, today its not possible with qemu builder because this iso its not attached.

hold this PR until packer 1.5 be released

Related Issue

closes #1252

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Chore (non-breaking change that does not add functionality or fix an issue)

Checklist:

• I have read the CONTRIBUTING document.
• I have run the pre-merge tests locally and they pass.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.
• All commits have been signed-off for the Developer Certificate of Origin.

[bugbuilder]

I could split this changes:

1. Just for the additional device
2. Another for the disk_size as string and the other templates, check backwards-breaking: Qemu builder disk size as a string #1253

The second one needs to adapt the rakefile for the CI.

Sorry for didn't test it first.

[bugbuilder]

I run the test with the packer master version and works as expected.

You'll need to updated your ci to use the latest packer version (1.5) at this moment your using packer 1.4.2.

[bugbuilder]

closing because packer revert this change.