Add integration test for PKCS#11 module

[simo5]

Description

Add an integration test to the cdylib crate using the rust-cryptoki library to act as a client to the PKCS#11 shared library.

This finally establishes end-to-end testing, of the actual pkcs#11 driver generated from the cdylib crate which is what is used by users.

The rust-cryptoki crate is used to drive the testing.

Checklist

• Test suite updated with functionality tests
• Test suite updated with negative tests
• Rustdoc string were added or updated
• CHANGELOG and/or other documentation added or updated
• This is not a code change

Reviewer's checklist:

• Any issues marked for closing are fully addressed
• There is a test suite reasonably covering new functionality or modifications
• This feature/change has adequate documentation added
• A changelog entry is added if the change is significant
• Code conform to coding style that today cannot yet be enforced via the check style test
• Commits have short titles and sensible text
• Doc string are properly updated

[Jakuje]

aside of the inline comment, lgtm

[simo5]

I fixed the issue with the committed database but also made integration tests optional.

To run them you have to explicitly run cargo build before you run cargo test in order to generate the .so, so on a clean project running just cargo test would fail.

With the integration tests made optional, cargo test will run all other tests fine on a clean tree. I think this is a better experience.

I tried to make the dependency on cryptoki optional too, but dev-dependencies can't be made optional so we'll have to keep it as it is.