Write linux proxy logs to mount folder (#8295)

* ensure we write the log to the same root directory as what is being used for the proxy invocation

* fix spacing

* we should write these proxy logs to the same root folder that we start the proxy in

Author: scbedd

eng/common/testproxy/test-proxy-tool.yml

@@ -63,8 +63,8 @@ steps:
 
     # nohup does NOT continue beyond the current session if you use it within powershell
     - bash: |
-        nohup $(Build.BinariesDirectory)/test-proxy/test-proxy &>$(Build.SourcesDirectory)/test-proxy.log &
-        
+        nohup $(Build.BinariesDirectory)/test-proxy/test-proxy &>${{ parameters.rootFolder }}/test-proxy.log &
+
         echo $! > $(Build.SourcesDirectory)/test-proxy.pid
         echo "##vso[task.setvariable variable=PROXY_PID]$(cat $(Build.SourcesDirectory)/test-proxy.pid)"
       displayName: "Run the testproxy - linux/mac"