Delete corrupt cache entries from ~/.gerritcodereview/buck-cache

If the SHA-1 does not match the downloaded file content, delete the
file from the cache. This allows a user to fix whatever connectivity
problem led to the corruption and re-run buck build to download
the correct content.

Change-Id: I2f72fb2b187675ec9d5cda650d8982bc93a00189

tools/download_file.py

@@ -17,7 +17,7 @@ from __future__ import print_function
 
 from hashlib import sha1
 from optparse import OptionParser
-from os import link, makedirs, path, symlink
+from os import link, makedirs, path, remove, symlink
 import shutil
 from subprocess import check_call, CalledProcessError
 from sys import stderr
@@ -135,12 +135,15 @@ if not path.exists(cache_ent):
 if args.v:
   have = hashfile(cache_ent)
   if args.v != have:
-    o = cache_ent[len(root_dir) + 1:]
     print((
       '%s:\n' +
       'expected %s\n' +
-      'received %s\n' +
+      'received %s\n') % (src_url, args.v, have), file=stderr)
-      '         %s\n') % (src_url, args.v, have, o), file=stderr)
+    try:
+      remove(cache_ent)
+    except OSError as err:
+      if path.exists(cache_ent):
+        print('error removing %s: %s' % (cache_ent, err), file=stderr)
     exit(1)
 
 exclude = []