Always calculate the absolute path for the output directory

[juliogonzalez]

Preparing the documentation on Friday, I noticed that if I used -o package, the build worked, but the package directory didn't contain anything.

Seems this is fixed by always specifying absolute paths when preparing the bind mount for podman, so this PR is precisely calculating that absolute path.

build/en/pdf/uyuni_quickstart_guide.pdf
build/en/pdf/uyuni_client-configuration_guide.pdf
build/en/pdf/uyuni_installation-and-upgrade_guide.pdf
build/en/pdf/uyuni_administration_guide.pdf
build/en/pdf/uyuni_retail_guide.pdf
mkdir -p build/packages
mv uyuni-docs_en.tar.gz uyuni-docs_en-pdf.tar.gz build/packages
[INFO] You can find find the build output at /home/juliogonzalez/Documents/development/git/suse/uyuni-docs-helper/package/build

real    3m49,440s
user    0m0,513s
sys     0m0,279s

$ ls -l /home/juliogonzalez/Documents/development/git/suse/uyuni-docs-helper/package/build
total 8
drwxr-xr-x 5 juliogonzalez users 4096 ago 26 09:49 en
drwxr-xr-x 2 juliogonzalez users 4096 ago 26 09:49 packages