Modify path of python wheels to be installed. (sonic-net#240)

**- What I did**
Modify path of python wheels to be installed as per changes in sonic-buildimage repo.
**- How I did it**
Modify path of swsssdk and sonic-py-common python wheels.

azure-pipelines.yml

@@ -46,8 +46,8 @@ stages:
         set -ex
         sudo apt-get -y purge libhiredis-dev libnl-3-dev libnl-route-3-dev
         sudo dpkg -i ../target/debs/buster/{libswsscommon_1.0.0_amd64.deb,python3-swsscommon_1.0.0_amd64.deb,libnl-3-200_*.deb,libnl-genl-3-200_*.deb,libnl-nf-3-200_*.deb,libnl-route-3-200_*.deb,libhiredis0.14_*.deb}
-        sudo python3 -m pip install ../target/python-wheels/swsssdk*-py3-*.whl
-        sudo python3 -m pip install ../target/python-wheels/sonic_py_common-1.0-py3-none-any.whl
+        sudo python3 -m pip install ../target/python-wheels/buster/swsssdk*-py3-*.whl
+        sudo python3 -m pip install ../target/python-wheels/buster/sonic_py_common-1.0-py3-none-any.whl
         python3 setup.py bdist_wheel
         cp dist/*.whl $(Build.ArtifactStagingDirectory)/
       displayName: "Build"