Improve error handling.

If the response to the HTTP request isn't 200 (success), then don't save
the response, and don't call the callback.

Additionally, only retry in the case of HTTPException. This allows using
Ctrl-C to work correctly (and easily).

scripts/python/terrasync.py

@@ -22,7 +22,7 @@
 
 import urllib, os, hashlib
 from urllib.parse import urlparse
-from http.client import HTTPConnection, _CS_IDLE
+from http.client import HTTPConnection, _CS_IDLE, HTTPException
 from os import listdir
 from os.path import isfile, join
 
@@ -54,7 +54,7 @@ class HTTPGetter:
 
         try:
             self.doGet(httpGetCallback)
-        except:
+        except HTTPException:
             # try to reconnect once
             #print("reconnect")
             self.httpConnection.close()
@@ -117,6 +117,9 @@ class HTTPDownloadRequest(HTTPGetCallback):
         self.mycallback = callback
 
     def callback(self):
+        if self.result.status != 200:
+            return
+
         with open(self.dst, 'wb') as f:
             f.write(self.result.read())