Implement chacha20-poly1305@openssh.com cipher using libgcrypt

This series enables use of fast ChaCha20 and Poly1305 implementations provided by libgcrypt. Libgcrypt has supported ChaCha20 and Poly1305 since 1.7.0 version.

Commits in series:

• tests: add crypto unittest for chacha20poly1305
  • Adds test vector for chacha20poly1305@openssh.com
• libgcrypt: Implement chacha20-poly1305@openssh.com cipher using libgcrypt
• libgcrypt: fix cipher handle leaks on setkey error paths
  • Fixes resource leak on error path noticed while working with libgcrypt.c