build-unit-test-docker: Add function2 to stdplus
build-unit-test-docker: Add function2 to stdplus

Header only upgrade for uses of std::function that can be converted.

Change-Id: I5f43a461c0446258c5456055569a6ed8c3c4d229
Signed-off-by: William A. Kennington III <30fff5198f4d10ca1117e5f3ec82f3b4b8900d81@google.com>

openbmc/openbmc-build-scripts,openbmc/openbmc-build-scripts