Add unzip runtime dependency to lua package (#8831)

* Add unzip to lua-luaposix

I ended up on an [Ubuntu] system that hadn't had unzip employed
and discovered lua-luaposix requires it (while buildig Lmod).

Closes #8533

* Move unzip prereq to lua, type=run

Rather than touching up each of the lua rocks (packages)
that need unzip, make it available as a run dependency in
lua.

Tested by building lmod on a minimal Ubuntu system.

var/spack/repos/builtin/packages/lua/package.py

@@ -49,6 +49,8 @@ class Lua(Package):
 
     depends_on('ncurses')
     depends_on('readline')
+    # luarocks needs unzip for some packages (e.g. lua-luaposix)
+    depends_on('unzip', type='run')
 
     resource(
         name="luarocks",