tests: improve qubes_basdir_patching
tests: improve qubes_basdir_patching

File storage pool use qubes.config.qubes_base_dir, not
qubes.config.system_path, so patch that too.

QubesOS/qubes-core-admin,woju/qubes-core-admin,QubesOS/qubes-core-admin,QubesOS/qubes-core-admin,woju/qubes-core-admin,woju/qubes-core-admin,marmarek/qubes-core-admin,woju/qubes-core-admin,marmarek/qubes-core-admin,marmarek/qubes-core-admin