Add Ubuntu 26.04 support for OSMorphing minions

[mihaelabalutoiu]

This PR implements the following changes:

• Remove the nested shell wrapper from the apt-get command;
• Improve shell quoting for GRUB configuration commands:
  • set_grub_value placed quotes by hand when building its sed scripts, so values containing spaces or quotes could be split into separate options instead of reaching sed as a single argument.
• Improve environment variable handling in OSMount tools:
  • the OSMount setup commands relied on sudo -E to forward the proxy configuration to the package managers, which does not work on sudo implementations that do not support the flag.
• Improve environment variable handling for chroot commands:
  • sudo-rs, the default sudo on Ubuntu 26.04, does not implement the -E flag, so proxy variables no longer reached commands run inside the chroot. They are now passed through env(1), which chroot(1) preserves.
• Add env command availability check on OSMorphing hosts;
• Disable pty allocation for SSH commands
• Sever mount propagation on OSMorphing chroot binds:
  • Systemd uses shared mount propagation, allowing mounts created under /proc, /sys, /dev or /run on the minion to propagate into the OSMorphing chroot.
  • On Ubuntu 26.04 this can leave systemd credential mounts under /run busy and cause the final umount -R to fail with target is busy.

[petrutlucian94]

osmount tools set the DEBIAN_FRONTEND env variable as part of the setup call. The osmorphing tools do not have a setup method but I think we can move it to the __init__ method.

uninstall_packages needs it as well and it's cleaner to set this as part of the constructor as opposed to install_packages / uninstall_packages. Modifying the shared _environment field as a side effect here isn't a clean approach.

[mihaelabalutoiu]

Gotcha, I updated the code, moved it to the constructor, so it covers uninstall_packages too and the side effect is gone from install_packages. Please take a look now, thank you!