Fix bug AttributeError: type object 'SaltCloudExecutionTimeout' has no a...

Fix bug AttributeError: type object 'SaltCloudExecutionTimeout' has no attribute '__code__'

The code in botocore_aws.py's __virtual__() function had a bug (see error message above).  This was due to the fact that the SaltCloudExecutionTimeout Exception class does not contain the words "Error" or "Exception" so it was not considered as an exception.  I started by adding the words "Timeout" and "Failure" to the list, but then I thought that this was not very robust code.  I suggest just checking that the object is a callable and that it has the __code__ attribute.