[sonic-mgmt] upgrade paramilo to version 2.7.1 (#4750)

spytest requires higher paramiko version. Fix it to 2.7.1.

Signed-off-by: Ying Xie <ying.xie@microsoft.com>

Author: yxieca

dockers/docker-sonic-mgmt/Dockerfile.j2

@@ -51,7 +51,7 @@ RUN pip install ipaddr \
                 pysnmp==4.2.5 \
                 jinja2==2.7.2 \
                 cffi==1.10.0 \
-                paramiko==2.1.2 \
+                paramiko==2.7.1 \
                 passlib \
                 ipython==5.4.1 \
                 virtualenv \