Add AWS EC2 backend driver support

[ezamriy]

We need to implement an AWS EC2 backend driver for our Test System due to the following reasons:

• There are some packages that should be tested on AWS: kernel with ENA drivers, cloud-init.
• Spot instances are quite cheap and can be used when our hardware resources are overloaded.
• Graviton machines seem to be the most popular ARM hosting solution nowadays so we need to run our kernel/bootloader tests there.