adb: work around adbd push bug.

We shipped (well, are about to ship) an adbd that spuriously fails to
create directories upon push. Work around this in the adb client by
running a mkdir on all of the directories we would have otherwise
created.

On devices where we perform the workaround, this coincidentally fixes
a historic bug where we failed to push empty directories.

Bug: http://b/25566053
Bug: http://b/110953234
Test: python test_device.py
Change-Id: I690ec356c206fed4e5ab2c681c5570c8b231e26b