REGTESTS: quic: set_ssl_cert.vtc supported by QUIC

REGTESTS: quic: set_ssl_cert.vtc supported by QUIC

ssl/set_ssl_cert.vtc was renamed to ssl/set_ssl_cert.vtci
to produce a common part runnable both for QUIC and TCP listeners.
Then set_ssl_cert.vtc files were created both under ssl and quic directories
to call this .vtci file with correct VTC_SOCK_TYPE environment values
("quic" for QUIC listeners and "stream" for TCP listeners);