Add optional singularity filesystem encryption

[iqmtestd]

and fix various problems with singularity image generation:

• klayout binary is included
• simplify install_deb_packages()
• no more shellcheck errors
• use docker in place of debootstrap

Issue #1306

[github-actions[bot]]

Test results

       5 files  ±0         5 suites  ±0   4m 3s :stopwatch: +14s    333 tests ±0     332 :heavy_check_mark: ±0  1 :zzz: ±0  0 :x: ±0  1 665 runs  ±0  1 660 :heavy_check_mark: ±0  5 :zzz: ±0  0 :x: ±0 

Results for commit ec094913. ± Comparison against base commit 51817e14.

:recycle: This comment has been updated with latest results.