Add a placehohlder for non-expanded identities

Expanding a string twice could lead to unwanted behaviour.
This solution creates a ssh_list (`opts.identites_non_exp`) to store the strings
before expansion and by using ssh_apply it moves the string to the
`opts.identities`. This way the expanded strings are separated.

Signed-off-by: Norbert Pocs <npocs@redhat.com>
Reviewed-by: Jakub Jelen <jjelen@redhat.com>
(cherry picked from commit 1ff893c914)

include/libssh/session.h

@@ -209,6 +209,7 @@ struct ssh_session_struct {
 #endif
     struct {
         struct ssh_list *identity;
+        struct ssh_list *identity_non_exp;
         char *username;
         char *host;
         char *bindaddr; /* bind the client to an ip addr */