The logic of the inline bash scripts of each job was sometimes
separated into the flatcar-scripts/jenkins/*.sh helpers but mostly
part of the Groovy file. This coupling had its advantages but also
downsides when special cases needed to be added for different release
versions. Other issues were that the inline scripts needed the
backslash character to be escaped twice and Jenkins was not good in
terminating the child processes when stopping a job. Having inline
bash scripts in Groovy also mandated the use of Jenkins to build and
release Flatcar Container Linux which hinders test builds in other CI
platforms.
Move the inline bash scripts fully to to the files in
flatcar-scripts/jenkins/ and create new ones for job that didn't have
a script there yet. Also invoke them through a systemd-run wrapper
script which ensures that all child processes are terminated and also
sets up /opt/bin as additional path for the static lbzcat binary.
A workaround for bash 4 was needed to use a temporary file instead of
the <(cmd) bash feature which caused a strange syntax error, otherwise
the bash commands are moved as they are.
