s3:tests: Create a test directory for a clean test

s3:tests: Create a test directory for a clean test

The test fails on openSUSE Tumbleweed with:

NT_STATUS_FILE_IS_A_DIRECTORY opening remote file \foo\bar\testfile

This cleans up the code to create a directory 'test' which can be
completely removed so nothing will stay behind. It also makes sure that
all parent directories are created and the files have some content.

https://bugzilla.samba.org/show_bug.cgi?id=12721

Signed-off-by: Andreas Schneider <asn@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>
Autobuild-User(master): Jeremy Allison <jra@samba.org>
Autobuild-Date(master): Sat Apr  8 12:29:19 CEST 2017 on sn-devel-144