add support to `eessi_container.sh` for using `unionfs` overlay tool #77

Job	Run time
basic_checks (2023.06)	31s
make_sure_load_and_unload_work (2023.06, x86_64/amd/zen4, none)	41s
lmod_and_init_script_comparison (2023.06, x86_64/amd/zen4, accel/nvidia/cc80)	29s
make_sure_load_and_unload_work (2023.06, x86_64/amd/zen4, accel/nvidia/cc80)	1m 24s
lmod_and_init_script_comparison (2023.06, x86_64/amd/zen3, accel/nvidia/cc80)	38s
make_sure_load_and_unload_work (2023.06, x86_64/amd/zen2, none)	35s
make_sure_load_and_unload_work (2023.06, none, none)	36s
make_sure_load_and_unload_work (2023.06, none, accel/nvidia/cc80)	44s
make_sure_load_and_unload_work (2023.06, x86_64/amd/zen2, accel/nvidia/cc80)	33s
	6m 11s

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