IMPALA-767: Log errors from BaseSequenceScanner::ReadFileHeader()

This patch fixes our handling of Avro tables containing unsupported
types (i.e. complex types). In debug builds we would hit a DCHECK in
codegen, and in release builds we would silently fail in
ResolveSchemas. This patch fixes the DCHECK and propagates the error
properly, as well as removes some redundant logging from other
scanners.

Change-Id: I7f5dcd81404cd85ac1cbb950a2b6abd2d7f6161f
Reviewed-on: http://gerrit.ent.cloudera.com:8080/1902
Reviewed-by: Nong Li <nong@cloudera.com>
Tested-by: jenkins