BUG/MINOR: ssl: Stop passing dynamic strings as format arguments

BUG/MINOR: ssl: Stop passing dynamic strings as format arguments

gcc complains rightfully:

src/ssl_sock.c: In function ‘ssl_sock_prepare_all_ctx’:
src/ssl_sock.c:5507:3: warning: format not a string literal and no format arguments [-Wformat-security]
   ha_warning(errmsg);
   ^
src/ssl_sock.c:5509:3: warning: format not a string literal and no format arguments [-Wformat-security]
   ha_alert(errmsg);
   ^
src/ssl_sock.c: In function ‘cli_io_handler_commit_cert’:
src/ssl_sock.c:10208:3: warning: format not a string literal and no format arguments [-Wformat-security]
   chunk_appendf(trash, err);

Introduced in 8b453912ce9a4e1a3b1329efb2af04d1e470852e.