JobImpl uber checks for cpu are wrong

The cpu checks for uberizing have two issues:

1. the defaults are hardcoded instead of using the conf defaults
2. the comparison against the sys cpu size is using < instead of <=

    boolean smallCpu =
        (
            Math.max(
                conf.getInt(MRJobConfig.MAP_CPU_VCORES, 1), 
                conf.getInt(MRJobConfig.REDUCE_CPU_VCORES, 1)) < 
             sysCPUSizeForUberSlot
        );

Everything is defaulting to 1, so uber cpu checks are now disabled causing TestUberAM to fail.