CBQE-1049 Fix type and order of teardown call in backup_base

Change-Id: Ic32e8e06542926124921482043e33c252ba7b32f
Reviewed-on: http://review.couchbase.org/24872
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Deepkaran Salooja <deepkaran.salooja@globallogic.com>
Tested-by: Deepkaran Salooja <deepkaran.salooja@globallogic.com>