Detect and fix improper file ownership on launch

[blaedj]

This commit:

• detects a subset of what osquery will consider improper file
  perms/ownership on the extension binary
• tries to fix those errors

We could and perhaps should apply this to the entire root directory,
and this doesn't yet work on windows.

[directionless]

Tested and appears to work as advertised. Yay!

Digging at a test case, I don't see a homebrew provided command or docs that creates this error. But chown $USER does cause this problem, and it shows up in various suggestions

[blaedj]

            chown blaed ~/launcher_root_bad_perms
            sudo rm ~/launcher_root_bad_perms/kolide/bin/launcher
            sudo rm ~/launcher_root_bad_perms/kolide/bin/osquery-extension.ext

            cp ~/code/go/src/github.com/kolide/launcher/build/launcher ~/launcher_root_bad_perms/kolide/bin/
            cp ~/code/go/src/github.com/kolide/launcher/build/osquery-extension.ext ~/launcher_root_bad_perms/kolide/bin/

            sudo launchctl asuser 0 \
                 ~/launcher_root_bad_perms/kolide/bin/launcher \
                 -root_directory "~/launcher_root_bad_perms/kolide" \
                 -hostname localhost:5000 \
                 -enroll_secret_path secret.txt \
                 --osqueryd_path "~/launcher_root_bad_perms/kolide/bin/osqueryd" \
                 --insecure \
                 --insecure_transport \
                 -transport jsonrpc \
                 -autoupdate \
                 -update_channel="beta" \
                 -debug \
                 -with_initial_runner \
                 -disable_control_tls 

that's the script I used (or close to it) to test this out.