vol: Fix ntops to provide expected semantics

vol: Fix ntops to provide expected semantics

nt_open() can be asked to open a file with a path containing
directory components that do not yet exist.  Modify nt_open()
to automatically create directories if necessary.

nt_read() and nt_pread() should not treat partial reads due
to reaching EOF as an error.  Instead, return the bytes read.

Reviewed-on: http://gerrit.openafs.org/3666
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
(cherry picked from commit 714b3ffb2258b316621415c2e81372dc48b4119d)

Change-Id: I4a4c8a4894aa25bec883154cb73d1ee24986ba15
Reviewed-on: http://gerrit.openafs.org/3828
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>