Add a fallback for CPU arch detection

`platform.processor()` seems to be returning '' a lot where it
wasn't before. Not sure why, but let's add a fallback to
`platform.machine()` to give us another shot at getting a value.

Signed-off-by: Adam Williamson <awilliam@redhat.com>

createhdds.py

@@ -43,6 +43,8 @@ from six.moves.urllib.request import urlopen
 # directory.
 SCRIPTDIR = os.path.abspath(os.path.dirname(sys.argv[0]))
 CPUARCH = platform.processor()
+if not CPUARCH:
+    CPUARCH = platform.machine()
 logger = logging.getLogger('createhdds')
 
 def handle_size(size):