HADOOP-14315. Python example in the rack awareness document doesn't work due to bad indentation

This closes #214

Signed-off-by: Akira Ajisaka <aajisaka@apache.org>

hadoop-common-project/hadoop-common/src/site/markdown/RackAwareness.md

@@ -91,12 +91,12 @@ sys.argv.pop(0)                                                  # discard name
 netmask = '255.255.255.0'                                        # set netmask to what's being used in your environment.  The example uses a /24
 
 for ip in sys.argv:                                              # loop over list of datanode IP's
-address = '{0}/{1}'.format(ip, netmask)                      # format address string so it looks like 'ip/netmask' to make netaddr work
-try:
-   network_address = netaddr.IPNetwork(address).network     # calculate and print network address
-   print "/{0}".format(network_address)
-except:
-   print "/rack-unknown"                                    # print catch-all value if unable to calculate network address
+    address = '{0}/{1}'.format(ip, netmask)                      # format address string so it looks like 'ip/netmask' to make netaddr work
+    try:
+        network_address = netaddr.IPNetwork(address).network     # calculate and print network address
+        print "/{0}".format(network_address)
+    except:
+        print "/rack-unknown"                                    # print catch-all value if unable to calculate network address
 ```
 
 bash Example