tests: shell: introduce the cache testcases directory

This directory is for testcases related to the nft cache.

Signed-off-by: Arturo Borrero Gonzalez <arturo@debian.org>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/tests/shell/testcases/sets/cache_handling_0 b/tests/shell/testcases/cache/0001_cache_handling_0
similarity index 100%
rename from tests/shell/testcases/sets/cache_handling_0
rename to tests/shell/testcases/cache/0001_cache_handling_0