[Service API] Environment variable without a value should be read from the host

[AmelBawa-msft]

Reference: http://task.ms/61479746

WSLC

PS C:\> wslc container run -e "APPDATA" --rm alpine:latest env
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
HOSTNAME=
HOME=/root

Docker

PS C:\src\wsl> docker container run -e "APPDATA" --rm alpine:latest env
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
HOSTNAME=d8fa2c04b016
APPDATA=C:\Users\USER_NAME\AppData\Roaming # < Missing in WSLC
HOME=/root

[github-actions]

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If this a feature request, please reply with '/feature'. If this is a question, reply with '/question'.
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How to collect WSL logs

Download and execute collect-wsl-logs.ps1 in an administrative powershell prompt:

Invoke-WebRequest -UseBasicParsing "https://raw.githubusercontent.com/microsoft/WSL/master/diagnostics/collect-wsl-logs.ps1" -OutFile collect-wsl-logs.ps1
Set-ExecutionPolicy Bypass -Scope Process -Force
.\collect-wsl-logs.ps1

The script will output the path of the log file once done.

If this is a networking issue, please use .\collect-wsl-logs.ps1 -LogProfile networking instead, following the instructions in Collect WSL logs for networking issues

Once completed please upload the output files to this GitHub issue.

See Collect WSL logs (recommended method).

If you choose to email these logs instead of attaching them to the bug, please send them to wsl-gh-logs@microsoft.com with the GitHub issue number in the subject, and include a link to your GitHub issue comment in the message body, and reply with '/emailed-logs'.