update_dependencies in run script fails to detect dependencies on macOS

[bartaz]

Originally reported as canonical/snapcraft.io#1057

When running ./run script on macOS dependencies are not correctly detected. Manually cleaning hash files or running ./run clean is required to install new dependencies.

./run serve
 
Yarn dependencies haven't changed. To force an update, delete .yarn.canonical-webteam-snapcraft-flask-048191a3.hash.
bash: md5: command not found
xargs: md5: No such file or directory
Pip dependencies haven't changed. To force an update, delete .pip.canonical-webteam-snapcraft-flask-048191a3.hash.

It seems that for some types of dependencies (pip at least: https://github.com/canonical-websites/snapcraft.io/blob/master/run#L322) md5 command is run inside of docker image, while md5_command is detected in host system.

If host system uses different md5 command then ubuntu in docker, detecting dependencies will fail.

[tbille]

@bartaz have you seen this issue again, please reach out if you have.

[bartaz]

I don't think we had any dependency changes recently for me to notice, but I'm pretty sure it's still around.