Fix pipeline error for vs image

Why I did it
PR checker failed to build vs image.

How I did it
Build vs image at first, and then build GNMI test container.

How to verify it
Create new PR and check build pipeline.

.azure-pipelines/azure-pipelines-build.yml

@@ -130,10 +130,10 @@ jobs:
               make $BUILD_OPTIONS ENABLE_ASAN=y target/docker-sonic-vs.gz
               mv target/docker-sonic-vs.gz target/docker-sonic-vs-asan.gz
             fi
+            make $BUILD_OPTIONS target/docker-sonic-vs.gz target/sonic-vs.img.gz target/docker-ptf.gz
             if [ $(gnmi_test_container) == yes ]; then
               make $BUILD_OPTIONS target/docker-gnmi-test.gz
             fi
-            make $BUILD_OPTIONS target/docker-sonic-vs.gz target/sonic-vs.img.gz target/docker-ptf.gz
             if [ $(Build.Reason) != 'PullRequest' ];then
               gzip -kd target/sonic-vs.img.gz
               SONIC_RUN_CMDS="qemu-img convert target/sonic-vs.img -O vhdx -o subformat=dynamic target/sonic-vs.vhdx" make sonic-slave-run