Use bundled SSL libraries instead of system OpenSSL (Closes: #921488)

It has been disputed whether MySQL and MariaDB can license-wise use
OpenSSL or not. Building with '-DWITH_SSL=bundled' makes the server use
YaSSL and the Connector/C use GnuTLS.

Once OpenSSL 3.0 is released, switch back to it.

Since OpenSSL is missing, libmariadb3 will lack the sha256_password plugin.