Rewrite loader linux/initrd entry relabelling without regex to improve reliability

[KaliumPuceon]

Replacing the regex-based loader entry fix with string parsing.

A user building RHEL images ran into issues with the initrd. It turns out that RHEL uses some patches that mean the initrd/linux files in RHEL are not installed to /boot, which trips up the original regex. The new fix doesn't rely on matching the path in boot, instead just finding the initrd/linux files and rewriting them in place.

This change also adds the pre-and-post fix loader entries to the debug logs.

Original bug report https://bugzilla.suse.com/show_bug.cgi?id=1208701

Fixes suse bsc#1208701

Changes proposed in this pull request:

• Replace loader fix regex with python string handling.

[schaefi]

Thanks for the work done here. As discussed internally on slack I appreciate the change. I'll do some tests. Could you please fix the white space issues reported by the linters ? Thanks much

@davidcassany if you can take a look at the changes would be great. I'm on vacation this week and will take a look when I'm back

[schaefi]

@davidcassany can you also take a look on the proposed changes ? Thanks much

[schaefi]

Given the last nit pick change got addressed, this looks good to me. Thanks for your effort

[Conan-Kudo]

Please squash all this into a single commit.

[Conan-Kudo]

@KaliumPuceon Can you put your pull request description in the commit message? Here's a suggested version:

Replace the regex-based loader entry fix with string parsing

A user building RHEL images ran into issues with the initrd. 
It turns out that RHEL uses some patches that mean the
initrd/linux files in RHEL are not installed to /boot, which trips
up the original regex. The new fix doesn't rely on matching the
path in boot, instead just finding the initrd/linux files and rewriting
them in place.

This change also adds the pre-and-post fix loader entries to the debug logs.

Reference: https://bugzilla.suse.com/1208701

Fixes suse bsc#1208701

[Conan-Kudo]

I just took care of it via squash merge.

[schaefi]

ok, this change now needs good testing through the integration test matrix. As it will be visible at boot time I would wish we can just trigger the build tests done by @dcermak somehow ? But I think we need Dan to do it. I will update kiwi in Staging today so that the integration tests rebuild