Resizing/Truncating returned lists

[daxpedda]

Pkcs11::get_slots_with_token, Pkcs11::get_all_slots and Pkcs11::get_mechanism_list currently truncate returned lists to account for changed sizes between querying the size and getting the list, a typical race condition.

There are two problems with this currently:

• Vec::resize is used instead of Vec::truncate for Pkcs11::get_slots_with_token and Pkcs11::get_all_slots
• Lists can also increase in size, which returns an error, it might be better to put it in a loop until the correct size is established

[ionut-arm]

Reopening this as the original PR was merged by mistake and then nuked from main.