[mgmt docker] move pycryptodome installation to the end of the docker…

… building (#4917)

* [mgmt docker] move pycryptodome installation to the end of the docker building

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

* pin down the version to current: 3.9.8

* comment

dockers/docker-sonic-mgmt/Dockerfile.j2

@@ -49,7 +49,6 @@ RUN pip install cffi==1.10.0 \
                 prettytable \
                 psutil \
                 pyasn1==0.1.9 \
-                pycryptodome \
                 pyfiglet \
                 pylint==1.8.1 \
                 pyro4 \
@@ -169,3 +168,7 @@ RUN ~/lib/azure-cli/bin/python -m pip install azure-keyvault==0.3.7 -U
 # Install Virtual Environment
 RUN python -m virtualenv --system-site-packages env-201811
 RUN env-201811/bin/pip install ansible==2.0.0.2
+
+# NOTE: There is an ordering dependency for pycryptodome. Leaving this at
+#       the end until we figure that out.
+RUN pip install pycryptodome==3.9.8