Fix arg parsing in Coverity script

The Coverity script still used some Python2-isms in argument parsing.
These didn't matter for today's Coverity runs, since the package is
called as a library from the nightly builder, but is important
as part of splitting nightly tarballs and Coverity.

Signed-off-by: Brian Barrett <bbarrett@amazon.com>

Author: bwbarrett

nightly-tarball/Coverity.py

@@ -169,7 +169,7 @@ def run_coverity(logger, build_root, source_tarball, config):
                         help='Coverity submission email address',
                         type=str)
 
-    for key, value in vars(parser.parse_args()).iteritems():
+    for key, value in vars(parser.parse_args()).items():
         if not value == None:
             config[key] = value