tests: bsim: gatt: ccc_store: Reproduce the subscription lost issue

Zephyr by default renews the characteristic value subscription on every
reconnection. If the ACL is disconnected in the middle of this
procedure, all the subscriptions waiting to be renewed are removed, even
if the device was successfully subscribed already.

Signed-off-by: Mariusz Skamra <mariusz.skamra@codecoup.pl>