build stops at or after UltraDefrag

[ngrigoriev]

Building off the latest version on Mac using the following command:

packer build --only=virtualbox-iso windows_2019_docker.json

The build seems to stop and not advancing even after several hours.

    virtualbox-iso: 2019-05-09T10:44:55 There are no applicable updates
    virtualbox-iso: 2019-05-09T10:44:55 Done Installing Windows Updates
    virtualbox-iso: End of Windows Updates log file C:\Windows\Temp\win-updates.log
    virtualbox-iso: C:\Users\vagrant>if "virtua" == "hyperv" (
    virtualbox-iso: echo "Skip compact steps in Hyper-V build."
    virtualbox-iso:  goto :eof
    virtualbox-iso: )
    virtualbox-iso: C:\Users\vagrant>if not exist "C:\Windows\Temp\7z1900-x64.msi" (powershell -Command "(New-Object System.Net.WebClient).DownloadFile('https://www.7-zip.org/a/7z1900-x64.msi', 'C:\Windows\Temp\7z1900-x64.msi')"  0<NUL )
    virtualbox-iso: C:\Users\vagrant>msiexec /qb /i C:\Windows\Temp\7z1900-x64.msi
    virtualbox-iso: C:\Users\vagrant>if not exist "C:\Windows\Temp\ultradefrag.zip" (powershell -Command "(New-Object System.Net.WebClient).DownloadFile('https://downloads.sourceforge.net/project/ultradefrag/stable-release/6.1.0/ultradefrag-portable-6.1.0.bin.amd64.zip', 'C:\Windows\Temp\ultradefrag.zip')"  0<NUL )
    virtualbox-iso: C:\Users\vagrant>if not exist "C:\Windows\Temp\ultradefrag-portable-6.1.0.amd64\udefrag.exe" (cmd /c ""C:\Program Files\7-Zip\7z.exe" x C:\Windows\Temp\ultradefrag.zip -oC:\Windows\Temp" )
    virtualbox-iso: 7-Zip 19.00 (x64) : Copyright (c) 1999-2018 Igor Pavlov : 2019-02-21
    virtualbox-iso: Scanning the drive for archives:
    virtualbox-iso: 1 file, 768893 bytes (751 KiB)
    virtualbox-iso: Extracting archive: C:\Windows\Temp\ultradefrag.zip
    virtualbox-iso: --
    virtualbox-iso: Path = C:\Windows\Temp\ultradefrag.zip
    virtualbox-iso: Type = zip
    virtualbox-iso: Physical Size = 768893
    virtualbox-iso: Everything is Ok
    virtualbox-iso: Folders: 5
    virtualbox-iso: Files: 166
    virtualbox-iso: Size:       2433004
    virtualbox-iso: Compressed: 768893
    virtualbox-iso: C:\Users\vagrant>if not exist "C:\Windows\Temp\SDelete.zip" (
    virtualbox-iso: powershell -Command "(New-Object System.Net.WebClient).DownloadFile('https://download.sysinternals.com/files/SDelete.zip', 'C:\Windows\Temp\SDelete.zip')"  0<NUL
    virtualbox-iso:  powershell -Command "(New-Object System.Net.WebClient).DownloadFile('https://vagrantboxes.blob.core.windows.net/box/sdelete/v1.6.1/sdelete.exe', 'C:\Windows\Temp\sdelete.exe')"  0<NUL
    virtualbox-iso: )
    virtualbox-iso: C:\Users\vagrant>if not exist "C:\Windows\Temp\sdelete.exe" (cmd /c ""C:\Program Files\7-Zip\7z.exe" x C:\Windows\Temp\SDelete.zip -oC:\Windows\Temp" )
    virtualbox-iso: C:\Users\vagrant>msiexec /qb /x C:\Windows\Temp\7z1900-x64.msi
    virtualbox-iso: C:\Users\vagrant>net stop wuauserv
==> virtualbox-iso: The Windows Update service is not started.
==> virtualbox-iso: More help is available by typing NET HELPMSG 3521.
    virtualbox-iso: C:\Users\vagrant>rmdir /S /Q C:\Windows\SoftwareDistribution\Download
    virtualbox-iso: C:\Users\vagrant>mkdir C:\Windows\SoftwareDistribution\Download
    virtualbox-iso: C:\Users\vagrant>net start wuauserv
    virtualbox-iso: The Windows Update service is starting.
    virtualbox-iso: The Windows Update service was started successfully.
    virtualbox-iso: C:\Users\vagrant>if "virtualbox-iso" NEQ "hyperv-iso" (
    virtualbox-iso: cmd /c C:\Windows\Temp\ultradefrag-portable-6.1.0.amd64\udefrag.exe --optimize --repeat C:
    virtualbox-iso:  cmd /c C:\Windows\System32\reg.exe ADD HKCU\Software\Sysinternals\SDelete /v EulaAccepted /t REG_DWORD /d 1 /f
    virtualbox-iso:  cmd /c C:\Windows\Temp\sdelete.exe -q -z C:
    virtualbox-iso: )
    virtualbox-iso: UltraDefrag 6.1.0, Copyright (c) UltraDefrag Development Team, 2007-2013.
    virtualbox-iso: UltraDefrag comes with ABSOLUTELY NO WARRANTY. This is free software,
    virtualbox-iso: and you are welcome to redistribute it under certain conditions.

I see the VM screen and the shell prompt there. I ran "tasklist" in that VM and here is what I see:

[clong]

Looks to be the same issue as this one: clong/DetectionLab#259

Some behavior in Packer 1.4.0 seems to have changed such that this hangs. Folks in that thread mentioned using start /wait in place of cmd /c which fixed it in my personal test, but I'm not sure how reliable that fix is. I wonder if there's a reason UltraDefrag is used in this repo over Windows' native defrag utility?