.travis.yml: added build --with-libssh

Signed-off-by: Nikos Mavrogiannopoulos <nmav@redhat.com>

.travis.yml

@@ -18,6 +18,7 @@ addons:
             - stunnel4
             - libidn2-0-dev
             - libssh2-1-dev
+            - libssh-dev
             - krb5-user
 
 matrix:
@@ -26,6 +27,10 @@ matrix:
           compiler: gcc
           dist: trusty
           env: T=normal C="--with-gssapi"
+        - os: linux
+          compiler: gcc
+          dist: trusty
+          env: T=normal C=--with-libssh
         - os: linux
           compiler: gcc
           dist: trusty