NodeManager fails to create containers when NM_LOG_DIR is not explicitly set in the Configuration

If the yarn configuration does not explicitly specify a value for the yarn.server.nodemanager.log.dir property, container allocation will fail on the NodeManager w/an NPE when the LocalDirAllocator goes to create the temp directory. In most of the code, we handle this by defaulting to /tmp/logs, but we cannot do this in the LocalDirAllocator context, so we need to set the default value explicitly in the Configuration.

Marking this as major b/c it's annoying to bump into it when you're getting your first MRv2 cluster up and running.