Defers the resolution of the SOURCE_DATE_EPOCH until the variable needs
to be actually realized with a value. The previous method of loading the
value in anonymous python had issues because it could occur before other
anonymous python functions that affect the location of the epoch file,
such as when a recipe uses AUTOINC/AUTOREV or allarch.bbclass.
Also adds more logging to help diagnose issues in the future.
[YOCTO #13763]
Signed-off-by: Joshua Watt <JPEWhacker@gmail.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
