Fix build tools image so make test in ztunnel can work without root

[krinkinmu]

There were a few issues that prevented me from being able to successfully run make test in ztunnel code:

1. Cargo directories are owned by root, while the make test runs cargo as non root; there was an attempt to give cargo directories in the build tools image broad enough permissions, so that user does not matter anymore (see Permissions on mount points need to be expanded #249) but when cargo directories were added on top of that we should have applied chmod recursively for this to work;
2. /var/run/netns directory just does not exist in the container
3. AppArmor transfer process to a restricted profile when it creates a new user namespace and the restrictions break the test.

This change addresses issues 1 and 2. To test that the change works I worked around the issue 3 by running this:

echo 0 | sudo tee /proc/sys/kernel/apparmor_restrict_unprivileged_userns

And once I did that, I was able to run make test in ztunnel repo successfully with the locally built build-tools image.

+cc @keithmattix @Stevenjin8 @jaellio

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[istio-testing]

Hi @krinkinmu. Thanks for your PR.

I'm waiting for a istio member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[keithmattix]

/ok-to-test