Sanity check that 'localhost' can be resolved before building Observatory

tools/observatory_tool.py

Index: tools/observatory_tool.py
diff --git a/tools/observatory_tool.py b/tools/observatory_tool.py
index 8450a07d62ad057fa6d88efcde39609fc21020b5..5936b8220517fe4c9c8da69a42d5724d44b3dec2 100755
--- a/tools/observatory_tool.py
+++ b/tools/observatory_tool.py
@@ -8,6 +8,7 @@ import argparse
 import os
 import platform
 import shutil
+import socket
 import subprocess
 import sys
 import utils
@@ -217,6 +218,13 @@ def ExecuteCommand(options, args):
     return -1;
 
 def main():
+  # Sanity check that localhost can be resolved.
+  try:
+    socket.gethostbyname('localhost')
+  except:
+    print("The hostname 'localhost' could not be resolved. Please fix your"
+          "/etc/hosts file and try again")
+    return -1
   # Parse the options.
   parser = BuildArguments()
   (options, args) = parser.parse_known_args()