Failure on downloading the image for QEMU

[mariyadavydova]

STR:

• Setup a new environment (or make sure that ~/.agentsea/vms doesn't exist)
• Start creating a device with QEMU provider
• Cancel the download process before it stops
• Start creating a device again

ER: The image is downloaded again.

AR: The creation of the device is stuck -- agentdesk tries to run this corrupted image and never succeeds. The only way out is to clean ~/.agentsea/vms