There are currently 5 different predefined exclude rules (.git, .gitignore, .DS_Store,
serverless.yaml, serverless.env.yaml) which will ensure that those files are not
included in the zipped archive. This test ensures this behavior.
Add zipping of handler directories. Add a walkDirSync method which collects all the
file paths in a directory (needed for the .zip file creation for "magic handlers") in a synchronous way.
Add generation of a unique .zip file so that two function .zip files won't collide.
Furthermore the .zip file is stored in a temp directory so that it won't pollute the service directory.