Multiple boto3 clients with a single botocore session is not thread safe

[smarlowucf]

Whether or not temporary credentials are used with ec2imgutils there's a chance for a session to be shared across multiple clients. This is not recommended based on boto3 documentation https://boto3.amazonaws.com/v1/documentation/api/latest/guide/resources.html?highlight=multithreading#multithreading-or-multiprocessing-with-resources.

This is in reference to the connect method on the EC2ImgUtils class https://github.com/SUSE-Enceladus/ec2imgutils/blob/master/lib/ec2imgutils/ec2imgutils.py#L45.

When using a temporary credential the session gets reused many times with new clients, otherwise the client is created which leaves it up to boto3/botocore to find an existing session or create a new one. As per the boto3 docs it's recommended to explicitly create a new session for every new client.

[smarlowucf]

Double checking this, a new session is already created in the default case https://github.com/SUSE-Enceladus/ec2imgutils/blob/master/lib/ec2imgutils/ec2imgutils.py#L59. The only thing to cleanup is to re-use the same client when supplying a session token.