configure, create and run LXC application containers

Changes for 0.14 - 2023-08-16T08:33:53Z

• t/03-setup.t: skipping \A regexp tests in older Perl versions
• t/06-update.t: another fix to count elements of hash in older Perl versions
• t/06-update.t: allowed different number of elements in 'mount_' hash tests