Trying to copy the image to different subscription (different tenant)

### **This is autogenerated. Please review and update as needed.**

## Describe the bug

**Command Name**
`az image copy
Extension Name: image-copy-extension. Version: 0.2.4.`

**Errors:**
```
Command '['/opt/az/bin/python3', '-m', 'azure.cli', 'group', 'exists', '--name', 'image-copy-rg', '--output', 'tsv', '--subscription', '46cb9d01-b5d1-4842-8034-748ef91dff6c']' returned non-zero exit status 1.
Traceback (most recent call last):
python3.6/site-packages/knack/cli.py, ln 215, in invoke
cmd_result = self.invocation.execute(args)
cli/core/commands/__init__.py, ln 631, in execute
raise ex
...
subprocess.CalledProcessError: Command '['/opt/az/bin/python3', '-m', 'azure.cli', 'group', 'exists', '--name', 'image-copy-rg', '--output', 'tsv', '--subscription', '46cb9d01-b5d1-4842-8034-748ef91dff6c']' returned non-zero exit status 1.
```

## To Reproduce:
Steps to reproduce the behavior. Note that argument values have been redacted, as they may contain sensitive information.

- _Put any pre-requisite steps here..._
- `az image copy --source-resource-group {} --source-object-name {} --target-location {} --target-resource-group {} --target-subscription {}`

## Expected Behavior

## Environment Summary
```
Linux-4.15.0-1077-azure-x86_64-with-debian-stretch-sid
Python 3.6.5
Installer: DEB

azure-cli 2.4.0 *

Extensions:
image-copy-extension 0.2.4

```
## Additional Context