tools: Add handle for automatically closing blobs
tools: Add handle for automatically closing blobs

This makes it harder to accidentally leak blob handles and cleans up the
code a little bit.

Change-Id: I49a1606a3360e6439a8c3d426de7006a138d330c
Signed-off-by: William A. Kennington III <30fff5198f4d10ca1117e5f3ec82f3b4b8900d81@google.com>

openbmc/phosphor-ipmi-flash