Unable to complete builds due to inability to delete project workspace

[karajas]

In the buildtools repo, the following error message causes a failure to clean the project workspace leading to a failed build.

3:06:41 Using context: Innerloop Windows Debug
13:06:42 Building remotely on Azure0328100701 (auto-win2012-20160325) in workspace D:\j\workspace\innerloop_prtest4ca7949f
13:06:42 [WS-CLEANUP] Deleting project workspace...
13:06:48
ERROR: [WS-CLEANUP] Cannot delete workspace: remote file operation failed: D:\j\workspace\innerloop_prtest4ca7949f at hudson.remoting.Channel@2aaf2a22:Azure0328100701: hudson.remoting.ChannelClosedException: channel is already closed
13:06:48 ERROR: Cannot delete workspace: remote file operation failed: D:\j\workspace\innerloop_prtest4ca7949f at hudson.remoting.Channel@2aaf2a22:Azure0328100701: hudson.remoting.ChannelClosedException: channel is already closed
13:06:48 [BFA] Scanning build for known causes...
13:06:48 [BFA] Scanning build for known causes...
13:06:48 [BFA] Found failure cause(s):
13:06:48 [BFA] Hung processs on target machine from category Infrastructure
13:06:48 [BFA] Done. 0s
13:06:48 Setting status of 38525666293756dc6fca04171a8125707c1414bc to FAILURE with url http://dotnet-ci.cloudapp.net/job/dotnet_buildtools/job/master/job/innerloop_prtest/264/ and message: 'Build finished. No test results found.'

/cc: @mmitche