DAFS: Request salvage on detach for volser

DAFS: Request salvage on detach for volser

When the volserver notices that a volume needs salvaging, mark
V_needsSalvaged. So when we VDetachVolume the volume, we can then just
request the salvage in the volume package.

Fix the VolClone salvaging code to do this as well, instead of using
the vol-private VRequestSalvage_r interface.

Change-Id: I9d48e4ea18fe4e3e2e1dc38593db4beb5ad79a84
Reviewed-on: http://gerrit.openafs.org/4452
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>