debian/postinst: make it POSIX compat
debian/postinst: make it POSIX compat


Former-commit-id: 70d08287873ef78deb86da5eee06c93799486b52 [formerly 38c3f54b5871f441d4a6f3d7f6917f94818beeb3]
Former-commit-id: 8060e9912aac66dbe74a90107eadaf265cda3b80
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine