Add a PyInstaller build for unsupported distros

[velovix]

This adds configuration to build the CLI as a PyInstaller executable along with the necessary supporting code. The PyInstaller executable would be an option for users of distributions whose package manager we don't have support for.

Since there's no automatic update mechanism available, this also implements a new self-update command that pulls the latest version of the CLI and replaces the current version with that one.

Unfortunately, this version of the CLI does not ship with its own version of Docker Compose. Packaging Compose into PyInstaller isn't straightforward, and it can't be run as a module because the Python interpreter is embedded in the binary. Instead, the expectation is that the user installs Compose with whatever mechanism they prefer.

See #13, which this PR does not fix on its own.

To-do Before Merge

• Figure out where the executables should be uploaded to
• Update the self-update command to pull from a real URL
• Manual testing
  • Ubuntu 18.04
  • Ubuntu 20.04
  • CentOS 7

[BryceBeagle]

You should give this exceptions more info:

import errno
import os

raise FileNotFoundError(errno.ENOENT, os.strerror(errno.ENOENT), filename)

[velovix]

Usually I'm down to provide a lot of information in exceptions, but for this use-case it would all go unused always. The caller always knows what file it's asking for and would never provide the message to the user directly because we want a translated, user-readable error. If you gotta use errno to use FileNotFoundError properly, maybe I should go back to a custom exception.

[BryceBeagle]

My vote is to add the errno information to the FileNotFoundError, but it's not a deal-breaker if it doesn't happen

[apockill]

Just make sure to check those boxes before merging!

[velovix]

Manual tests looking good!