Windows: alter nmtest CreateFile modes

Windows: alter nmtest CreateFile modes

Change -r to open the file for FILE_SHARE_READ

Change -w to open the file for FILE_SHARE_WRITE

Change -w to open the file twice.  Once for sequential access
and once for random access.

LICENSE MIT

Change-Id: I295a7e7408e7e7eac06901108a726fe9e94bf18f
Reviewed-on: http://gerrit.openafs.org/1016
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Jeffrey Altman <jaltman@openafs.org>
Reviewed-by: Asanka Herath <asanka@secure-endpoints.com>
Tested-by: Asanka Herath <asanka@secure-endpoints.com>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>