buildhistory_analysis: improve field handling robustness

Avoid errors when comparing changes for KEY = value files (package info
files and image-info.txt):

* Handle keys appearing and disappearing - this will help to handle PE
  in package info files (which is only written when it is not blank) and
  when we add additional fields in future.
* Handle when old value is 0 for numeric field (avoid division by zero)
* Report when numeric field was empty or missing rather than 0 (but
  still treat it as 0 for comparison purposes)

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

0 files changed, 0 insertions, 0 deletions