LTP:  ima_{conditionals,measurements}.sh enhancements

New releases of many distros (e.g. Debian, openSUSE Tumbleweed, SLES, ...) switched shell for 'nobody' user from
/bin/bash (or /bin/sh) to /usr/sbin/nologin. That effectively disables using 'sudo' or 'su'.

Review and test Petr Vorel's patch set to address the IMA LTP tests.

Reference: https://lore.kernel.org/linux-integrity/20251002083701.315334-1-pvorel@suse.cz/