[BP]:MB-16109 Relax the assertion check on snapshot_reader tests
[BP]:MB-16109 Relax the assertion check on snapshot_reader tests

As the writer can run and compact the file before the readers
create the snapshot instances, this change relaxes the assertion
check on the snapshot open operation.

Change-Id: I48c5b98aca8191d4373cb82fd202eb048356d71f

joliss/forestdb,joliss/forestdb,couchbase/forestdb,wurikiji/forestdb,hisundar/forestdb,wurikiji/forestdb,hisundar/forestdb,couchbase/forestdb