Fix os.mkdir race condition.

This code checks whether a dir exists before creating it. In between the
check and the mkdir call, it is possible that another process will have
created the directory. We have seen this bug occur many times in
practice during our 'repo init' tests.

Change-Id: Ia47d39955739aa38fd303f4e90be7b4c50d9d4ba

repo

@@ -110,6 +110,7 @@ REPO_MAIN = S_repo + '/main.py' # main script
 MIN_PYTHON_VERSION = (2, 6)     # minimum supported python version
 
 
+import errno
 import optparse
 import os
 import re
@@ -243,10 +244,10 @@ def _Init(args):
     _print("fatal: invalid branch name '%s'" % branch, file=sys.stderr)
     raise CloneFailure()
 
-  if not os.path.isdir(repodir):
-    try:
-      os.mkdir(repodir)
-    except OSError as e:
+  try:
+    os.mkdir(repodir)
+  except OSError as e:
+    if e.errno != errno.EEXIST:
       _print('fatal: cannot make %s directory: %s'
              % (repodir, e.strerror), file=sys.stderr)
       # Don't raise CloneFailure; that would delete the
@@ -325,18 +326,18 @@ def NeedSetupGnuPG():
 
 
 def SetupGnuPG(quiet):
-  if not os.path.isdir(home_dot_repo):
-    try:
-      os.mkdir(home_dot_repo)
-    except OSError as e:
+  try:
+    os.mkdir(home_dot_repo)
+  except OSError as e:
+    if e.errno != errno.EEXIST:
       _print('fatal: cannot make %s directory: %s'
              % (home_dot_repo, e.strerror), file=sys.stderr)
       sys.exit(1)
 
-  if not os.path.isdir(gpg_dir):
-    try:
-      os.mkdir(gpg_dir, stat.S_IRWXU)
-    except OSError as e:
+  try:
+    os.mkdir(gpg_dir, stat.S_IRWXU)
+  except OSError as e:
+    if e.errno != errno.EEXIST:
       _print('fatal: cannot make %s directory: %s' % (gpg_dir, e.strerror),
              file=sys.stderr)
       sys.exit(1)