MB-16215 Don't make assertion checks on I/O results.
MB-16215 Don't make assertion checks on I/O results.

As I/O errors can happen in various cases, we shouldn't expect I/O opeartions
to be successful all the time, but instead process errors more gracefully
without making assertion checks on them.

Change-Id: I68831bedfe1b2d5372e657f432ab0003d0523c91

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