rgw: lua, add support for lua packages to the lua manager

rgw: lua, add support for lua packages to the lua manager

Refactor lua manager, adding new {add,remove}_package(), and
list_packages() methods; and changing get(), put(), del() methods
to {get,put,del}_script().  Renaming class from *LuaScriptManager
to *LuaManager to be consistent with dual *script and *package
functionality.

Note: I considered keeping the existing *LuaScriptManager classes
as is and adding *LuaPackageManager classes, but that seemed/seems
like overkill to me.

Signed-off-by: Kaleb S. KEITHLEY <kkeithle@redhat.com>