Rearrange AWS initializer params to reflect that key_name is mandatory (#1131)
Rearrange AWS initializer params to reflect that key_name is mandatory (#1131)

Before this patch, the provider would initialize and then later fail when
attempting to allocate a resource, with:

2019-07-10 23:02:00 parsl.providers.aws.aws:495 [ERROR]  Request for EC2 resources failed : Parameter validation failed:
Invalid type for parameter KeyName, value: None, type: <class 'NoneType'>, valid types: <class 'str'>

After this patch, the initializer will fail when intializing the
AWSProvider, before the DFK is even loaded, and with an error message
that better reflects the missing mandatory parameter.
Parsl/parsl,Parsl/parsl,Parsl/parsl,Parsl/parsl