fix(wordpress): add --allow-root to wp cmd for docker based wp

[kotakanbe]

What did you implement:

Sometimes WordPress processes are running as root user on docker based wordpress site.
wp command warns below when run as root user.

root@6ec65aaa6dff:/var/www/html# /usr/local/bin/wp plugin list --path=/var/www/html  -allow-root
Error: YIKES! It looks like you're running this as root. You probably meant to run this as the user that your WordPress installation exists under.

If you REALLY mean to run this as root, we won't stop you, but just bear in mind that any code on this site will then have full control of your server, making it quite DANGEROUS.

If you'd like to continue as root, please run this again, adding this flag:  --allow-root

If you'd like to run it as the user that this site is under, you can run the following to become the respective user:

    sudo -u USER -i -- wp <command>

To avoid this warning, add --allow-root arg.

Type of change

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• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce.

Checklist:

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• Write tests
• Write documentation
• Check that there aren't other open pull requests for the same issue/feature
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• Pass the test by make test
• Provide verification config / commands
• Enable "Allow edits from maintainers" for this PR
• Update the messages below

Is this ready for review?: YES