DescribePackage permission error not propagated up when running package-application

When running package-application, intending to update an existing package but the DescribePackage IAM permission is missing; the command will incorrectly try to create a package and will then error out with this message: `An error occurred (ConflictException) when calling the CreatePackage operation: {"resourceId":"XXXXXXX","message":"Package with same name exists.","resourceType":"Package"}`

I believe this is because of the check on the subprocess run call of describe-package in [package_application()](https://github.com/aws/aws-panorama-cli/blob/main/panoramacli/panorama-cli#L766), anything other than a successful call is treated as if the package doesn't exist when it might actually be another error (IAM permissions, network, etc)

```
#Check if the package already exists
status, output = execute(['aws panorama describe-package --output json --package-id packageName/' + package_name])
if status != 0: #Create new package if the package doesn't exist
```

The lack of visibility on the real error caused some confusion for me when when debugging a failing panorama application update. I think a good solution might be removing the shell commands altogether and using boto3 which has full(ish?) Panorama support now?