MINOR: ssl/cli: 'show ssl cert' displays the chain

Display the subject of each certificate contained in the chain in the
output of "show ssl cert <filename>".
Each subjects are on a unique line prefixed by "Chain: "

Example:

Chain: /C=FR/ST=Paris/O=HAProxy Test Intermediate CA 2/CN=ca2.haproxy.local
Chain: /C=FR/ST=Paris/O=HAProxy Test Intermediate CA 1/CN=ca1.haproxy.local
1 file changed