kmod_module: use 'modname/aliasname' as key for hash

kmod_module: use 'modname/aliasname' as key for hash

1 alias may correspond to more than 1 module. This would cause a
conflict in the hash table when inserting a module there and bad things
could happen.

Now we use 'modname/aliasname' as key, '/aliasname' part being optional.
Internally kmod_module_new_from_alias() will setup a 'modname/aliasname'
string and pass to kmod_module_new_from_name() that will treat the case
with a '/' in the name.

User might call kmod_module_new_from_name() without any slashes, so the
key my not contain it.