classes/buildhistory: Add option to strip path prefix

Adds an option to strip a prefix from the paths reported in
buildhistory. This makes it easier to compare task signatures in the
build history when the builds were done from different directories.

Signed-off-by: Joshua Watt <JPEWhacker@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>