Ensure repo waits for child process to terminate

See http://stackoverflow.com/questions/7004687/os-exec-on-windows:

execv on Windows does not behave as on Linux, i.e. a new process is
spawned and the parent process terminates right away, which makes the
shell prompt come back too soon.

Change-Id: I1f8d23208765988629f081e9b949c67cf71c08ae

repo

@@ -120,6 +120,7 @@ GITC_FS_ROOT_DIR = '/gitc/manifest-rw/'
 
 import errno
 import optparse
+import platform
 import re
 import shutil
 import stat
@@ -887,7 +888,10 @@ def main(orig_args):
   me.extend(orig_args)
   me.extend(extra_args)
   try:
-    os.execv(sys.executable, me)
+    if platform.system() == "Windows":
+      sys.exit(subprocess.call(me))
+    else:
+      os.execv(sys.executable, me)
   except OSError as e:
     _print("fatal: unable to start %s" % repo_main, file=sys.stderr)
     _print("fatal: %s" % e, file=sys.stderr)