Fix pipeline apt-get purge error. (sonic-net#349)

* Fix pipeline apt-get purge error.

Author: liushilongbuaa

azure-pipelines.yml

@@ -33,11 +33,15 @@ steps:
     artifact: sonic-buildimage.vs
     runVersion: 'latestFromBranch'
     runBranch: 'refs/heads/$(BRANCH_NAME)'
+    patterns: |
+      **/*.whl
+      **/*.deb
+    path: '$(Build.ArtifactStagingDirectory)'
   displayName: "Download artifacts from latest sonic-buildimage build"
 
 - script: |
     set -xe
-    sudo apt-get -y purge libhiredis-dev libnl-3-dev libnl-route-3-dev
+    sudo apt-get -y purge libhiredis-dev libnl-3-dev libnl-route-3-dev || true
     sudo dpkg -i libyang_1.0.73_amd64.deb \
                  libnl-3-200_*.deb \
                  libnl-genl-3-200_*.deb \
@@ -46,7 +50,7 @@ steps:
                  libhiredis0.14_*.deb \
                  libswsscommon_1.0.0_amd64.deb \
                  python3-swsscommon_1.0.0_amd64.deb
-  workingDirectory: $(Pipeline.Workspace)/target/debs/bullseye/
+  workingDirectory: $(Build.ArtifactStagingDirectory)/target/debs/bullseye/
   displayName: 'Install Debian dependencies'
 
 - script: |
@@ -56,7 +60,7 @@ steps:
     sudo pip3 install sonic_yang_mgmt-1.0-py3-none-any.whl
     sudo pip3 install sonic_yang_models-1.0-py3-none-any.whl
     sudo pip3 install sonic_config_engine-1.0-py3-none-any.whl
-  workingDirectory: $(Pipeline.Workspace)/target/python-wheels/bullseye/
+  workingDirectory: $(Build.ArtifactStagingDirectory)/target/python-wheels/bullseye/
   displayName: 'Install Python dependencies'
 
 - script: |