gclient_utils.AskForData will use raw_input on Python 2 and input on Python 3.

Bug: 1063976
Change-Id: I93c059c4e4454d01787716b5a0a2641ad5253f53
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2116370
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>
Reviewed-by: Anthony Polito <apolito@google.com>
Auto-Submit: Edward Lesmes <ehmaldonado@chromium.org>