build-unit-test-docker: Build sdeventplus with meson
build-unit-test-docker: Build sdeventplus with meson

sdeventplus is moving to meson, so we should build it that way for our
project cache.

Tested:
    Builds and installs files that are usable by dependencies.

Change-Id: I238f69a74bae80b8818724776bd203fbc8b18eb1
Signed-off-by: William A. Kennington III <30fff5198f4d10ca1117e5f3ec82f3b4b8900d81@google.com>

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