SOLARIS: Use vn_renamepath when available

In Solaris 11.1, the signature of vn_setpath changes; it gains an
extra boolean_t argument called 'force'. Instead of trying to adapt to
it, call vn_renamepath() instead, which will do the correct thing and
call vn_setpath &co for us. vn_renamepath has existed since Solaris 10
Update 8, and is in all releases of Solaris 11. Only call it in
Solaris 11, since it makes the ifdefs easier, and there are no
problems with calling vn_setpath on Solaris 10.

Thanks to Frank Batschulat for all of the relevant information.

Reviewed-on: http://gerrit.openafs.org/8894
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
(cherry picked from commit 6c50960174f35d75fd50956e248318a9c826fca1)

Change-Id: Ifdc5bb7785b791d36dc1523421badd29d8df2faa
Reviewed-on: http://gerrit.openafs.org/8896
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Paul Smeddle <paul.smeddle@gmail.com>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>