FIX: Amazon

- Properly terminate the instances that should halt
- use try/except clause for the connection, as the S_OK S_ERROR are no
use in constructors
FIX: no need to pass a list of UniqueIDs 

The list is created if needed.
FIX: the stopInstances must return standard structure

Also catch any exception and return it in S_ERROR
Merge remote-tracking branch 'spossVMDIRAC/fixAmazonBis' into prod