fixes #25120 - use medium provider interface

[timogoebel]

This commit makes use of the new medium provider interface to build the full host image as the old way of calling the methods is deprecated and will be removed in 1.22.
The embedded PXElinux template is now rendered in it's own template scope (yay, new renderer!) so we can avoid ugly gsub string replacement hacks.

This also prepares foreman_bootdisk for frozen strings.

And all of this removes this loop, which is very hard to digest:

foreman_bootdisk/app/services/foreman_bootdisk/iso_generator.rb

Lines 23 to 31 in 15ed6d9

	files.map! do |bootfile_info|
	bootfile_info.map do |f|
	suffix = f[1].split('/').last
	iso_f0 = iso9660_filename(f[0].to_s + '_' + suffix)
	tmpl.gsub!(f[0].to_s + '-' + suffix, iso_f0)
	ForemanBootdisk.logger.debug("Boot file #{iso_f0}, source #{f[1]}")
	[iso_f0, f[1]]
	end
	end

[lzap]

This test is actually for iso9660_filename to make sure that filenames gets shortened to maximum size for ISO format, can you keep it in some way or another? Note boot/RedHatEnterpriseLinuxAtomic-7.3-x86_64 -> BOOT/NUXATOMIC_7_3_X86_64_VMLINUZ (shortened automatically).

[timogoebel]

Sure, I can add some tests for iso9660_filename method. We should definitely have them.

[lzap]

Yep should be probably a unit test, whatever you prefer.

[timogoebel]

@lzap: added the unit test.

[lzap]

I was able to generate all images just fine, thanks!

[timogoebel]

Nice, standby for the next chores. :-)