In I8658a2b0, the very change where I added support for building
without Eclipse, I justified not handling a missing buck.properties on
the basis of it's always there if you're using Eclipse. Well that was
wrong.
Just ignore missing buck.properties. This doesn't handle the case
where buck is not on $PATH, but that's harder to do unless we build
buck.properties into the war, which we'd rather not as it makes the
wars non-hermetic across machines.
Change-Id: Iadd149cdc8bf3bd7ac574e4e75e06a44ea25a42f
bba19b0bc2