fix ingesting of init tarball

[boegel]

No description provided.

[boegel]

echo ${tar_first_file} | head -n 2 doesn't make much sense, since ${tar_first_file} is guaranteed to only be a single line

For compat layer tarball, this happens to work:

$ tar tf eessi-2023.06-compat-linux-aarch64-1686750806.tar.gz | head -n 1
2023.06/compat/linux/aarch64/
$ tar tf eessi-2023.06-compat-linux-aarch64-1686750806.tar.gz | head -n 1 | head -n 2 | tail -n 1 | cut -d/ -f2
compat

Likewise for software tarballs:

$ tar tf eessi-2023.06-software-linux-aarch64-neoverse_n1-1687302831.tar.tar | head -n 1
2023.06/software/linux/aarch64/neoverse_n1/.lmod/lmodrc.lua
$ tar tf eessi-2023.06-software-linux-aarch64-neoverse_n1-1687302831.tar.tar | head -n 1 | head -n 2 | tail -n 1 | cut -d/ -f2
software

Doesn't work for init tarball created with create_directory_tarballs though:

$ tar tf eessi-2023.06-init-1687437311.tar.gz | head -n 1
2023.06/
[$ tar tf eessi-2023.06-init-1687437311.tar.gz | head -n 1 | head -n 2 | tail -n 1 | cut -d/ -f2

With the fix, it does work fine:

$ tar tf eessi-2023.06-init-1687437311.tar.gz | head -n 2 | tail -n 1 | cut -d/ -f2
init

$ tar tf eessi-2023.06-software-linux-aarch64-neoverse_n1-1687302831.tar.tar | head -n 2 | tail -n 1 | cut -d/ -f2
software

$ tar tf eessi-2023.06-compat-linux-aarch64-1686750806.tar.gz | head -n 2 | tail -n 1 | cut -d/ -f2
compat

Although avoiding the double use of tar tf makes sense, it doesn't matter too much, since it's a quick operation, even for large tarballs.

[bedroge]

Lgtm