[hab-plan-build] Normalize file checksums before comparison
[hab-plan-build] Normalize file checksums before comparison

This changes our checksum comparison to be case-insensitive, allowing
user to use hexadecimal representations of the checksum that use
uppercase letters.

Fixes #5427

Signed-off-by: Steven Danna <9ce5770b3bb4b2a1d59be2d97e34379cd192299f@chef.io>

habitat-sh/habitat,rsertelon/habitat,habitat-sh/habitat,habitat-sh/habitat,rsertelon/habitat,rsertelon/habitat,habitat-sh/habitat,habitat-sh/habitat,habitat-sh/habitat,habitat-sh/habitat,rsertelon/habitat,rsertelon/habitat,rsertelon/habitat,rsertelon/habitat,habitat-sh/habitat