example, tests: fix ssh2 to correctly return failure

Before this patch ssh2 and test_ssh2 returned success even if the session
failed at `libssh2_session_handshake()` or after.

This patch depends on cda41f7, that fixed
running test_ssh2 on Windows via sshd_fixture.

Cherry-picked from libssh2#1017

Author: vszakats

example/ssh2.c

@@ -137,6 +137,8 @@ int main(int argc, char *argv[])
         goto shutdown;
     }
 
+    rc = 1;
+
     /* At this point we have not yet authenticated.  The first thing to do
      * is check the hostkey's fingerprint against our known hosts Your app
      * may have it hard coded, may go to a file, may present it to the

tests/test_ssh2.c

@@ -157,6 +157,8 @@ int main(int argc, char *argv[])
         } while(1);
     }
 
+    rc = 1;
+
     /* At this point we have not yet authenticated.  The first thing to do
      * is check the hostkey's fingerprint against our known hosts Your app
      * may have it hard coded, may go to a file, may present it to the