libadmin: Don't try to release garbage connection

In bos_ServerOpen, initalise the contents of bos_server structure
to 0 using calloc, so that if we jump to the error handling stuff
before they are assigned real values we don't end up trying to
release garbage.

Change-Id: I687d0b637833a08425e75391eb92a2dd4a150301
Reviewed-on: http://gerrit.openafs.org/9163
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Chas Williams - CONTRACTOR <chas@cmf.nrl.navy.mil>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>