jsoncheck: fix _indent_note for pre-formatted strings

Current versions of demjson return pre-formatted, pre-indented strings.
Line wrapping them results in strings that are harder to read.

With this patch, _indent_note splits strings into lines before indenting
and (if necessary) line wrapping them.

blueprint modularize-doctest
Change-Id: If7023f825c76bec16980dc84283da446c18a82b7
Merge "jsoncheck: fix _indent_note for pre-formatted strings"