Advanced variable injection

[mattsb42-aws]

If environment variable values being injected contain special characters, notably any of ", ', \, and probably more, shlex gets very confused when we attempt to split the command after injection.

The current flow is:

1. Inject values
2. shlex.split
3. shlex.quote

I think that the correct approach here might simply be to:

1. shlex.split (keeping Add Windows testing and validate command processing #5 in mind)
2. Inject values in each split command
3. shlex.quote

[mattsb42-aws]

point to investigate:

Since we're explicitly not passing the command to the shell in the subprocess.run execution, we probably do not need to shlex.quote the values. Test this and make sure; if we don't need to, don't.