Try to flush vnodes in FBSD's unmount, bailing if necessary
vflush() actually returns something! Check if we get EBUSY,
and don't continue if so. Also, actually call vflush on FBSD80_ENV.
Note that we currently leak refs on our root vnode, so this means
umount will fail unless it uses -f, for now.
Change-Id: I8f02ebfa127409f0e8567f3efa7eccf491147cbd
Change-Id: Iaa4666f1004b49b69a82c778a3de60633fac880f
Reviewed-on: http://gerrit.openafs.org/2214
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>