Fix logging in cfn-init and cfn-signal

logging.getLogger() was called with a wrong name in the cfn scripts. As
a result, the cfn_helper module logged everything to stderr.

Change-Id: I3447291b202887aa09b0f0cb01764708683e7821
Closes-Bug: #1269355
Merge "Fix logging in cfn-init and cfn-signal"