Guess the right template from /etc/os-release

[dcermak]

This PR adds a few patches from openSUSE's fork to support guessing the correct template from /etc/os-release

[ekohl]

This reads well to me, but I'd feel better if #112 was merged and this rebased so CI could agree.

[ekohl]

#112 was merged. Would you mind rebasing?

[voxik]

Not objecting the intent of this PR, but I'd be a bit happier, if the functionality lived somewhere outside of the executable. This way, it would be better testable. Of course if there was test case attached, it would be even better.

[voxik]

Hmm, looking on the PR in more detail, I am confused what is the purpose. We are already querying /etc/os-release:

gem2rpm/lib/gem2rpm/distro.rb

Lines 72 to 75 in 91b38c8

	def self.release_files
	@release_files ||=
	Dir.glob('/etc/{os-release,*{_version,-release}}*').uniq.select { |e| File.file? e }
	end

and

gem2rpm/lib/gem2rpm/distro.rb

Lines 27 to 36 in 91b38c8

	# Try os-release first.
	if (os_release_files = grouped_release_files['os-release'])
	content = File.open(os_release_files.first, Gem2Rpm::OPEN_MODE, &:read)
	begin
	os_release.os = content[/^ID=['"]?(.*?)['"]?$/, 1].to_sym
	os_release.version = content[/^VERSION_ID=['"]?(.*?)['"]?$/, 1]
	rescue
	end
	end

So this would be step backward.