PBS-39 feature: Add binlog encryption config and keyring support (part 5)

[percona-ysorokin]

https://perconadev.atlassian.net/browse/PBS-39

Added new static library 'opensslpp' which is intended to include c++ wrappers for OpenSSL cryptographic primitives.

The initial version includes:

• 'opensslpp::crypto_rng' class that provides random cryptographically-strong byte sequences generation (based on 'RAND_butes()' API call).
• 'opensslpp::cipher_context' class that provides a convenient way of encrypting / decrypting data with various algorithms (e.g. 'AES'), key lengths (e.g 128, / 192 / 256 bit), and in various modes (e.g. 'ECB', 'CBC', 'CTR', 'GCM'). It is based on 'EVP_CIPHER_CTX'.
• 'opensslpp::core_error' exception class that automatically extracts error message from the OpenSSL subsystem (via the 'ERR_get_error()' call)

Currently we support only the following encryption modes:

• 'ECB' - does not need IV, does not generate / verify tag, operates on blocks only (16 bytes)
• 'CBC' - needs IV, does not generate / verify tag, operates on blocks only (16 bytes)
• 'CTR' needs IV, does not generate / verify tag, operates on byte sequences of any size.
• 'GCM' needs IV, generates / verifies tag, operates on byte sequences of any size.

For both 'ECB' and 'CBC' modes we deliberately disable padding.

Added tho new unit tests:

• 'crypto_rnd_test.cpp' (BOOST_TEST_MODULE CryptoRndTests)
• 'cipher_context_test.cpp' (BOOST_TEST_MODULE CipherContextTests)