MB-8990: On OSX, reports directory should be under bin

Since cbhealthchecker sits right under bin directory under OSX,
we need to put reports directory right under bin directory too.

Change-Id: I5170bedae85fa8719cb8047c869f070cfb7dbca1
Reviewed-on: http://review.couchbase.org/28641
Tested-by: Bin Cui <bin.cui@gmail.com>
Reviewed-by: Bin Cui <bin.cui@gmail.com>