racing commands in hammer prepare-system

Commands that are expected to run synchronously are not waited for, resulting in unexpected races.

I saw a job failure caused by this once, and @manu also failed to prepare-system once when building an AMI.

Described in more detail by @manu. Quoting:

Recently introduced hammer.py temp folder changes (new path and cleanup) caused me troubles with building AMI for Ubuntu 22.04

Reason: execute('rm -rf ~/.hammer-tmp') is deleting things that are still needed to finish the previous command

==> amazon-ebs: [HAMMER]  2022-12-12 17:53:36,306 >>>>> Executing sudo make install in /.hammer-tmp/libyang/build
==> amazon-ebs: [HAMMER]  2022-12-12 17:53:36,307 [Errno 2] No such file or directory: '/.hammer-tmp/libyang/build'

Solution: I solved it by removing the rm -rf but it can probably be solved by adding interactive=True to execute() calls like execute('whatever_command', interactive=True) which will force execute() function to wait for the process to finish via p.wait() (p.communicate() could also be used) as it uses p = subprocess.Popen() for the command execution

BTW I would expect more issues as subprocess.Popen() is used for almost every execution of the "command" in hammer.py