Describe the bug
OSUtils.cpuUsage() function will produce NumberFormatException if cpuUsage() function returns 0.0 / 0.0 = NaN.

To Reproduce
When I start my WorkerServer in my MacOS, it will schedule to produce a heartbeat signal to zk, and it will produce NFE when get cpuUsage() result equals NaN(0.0 / 0.0) from oshi.AbstractCentralProcessor#getSystemCpuLoad().

Screenshots

Which version of Dolphin Scheduler:
-[dev]

**Requirement or improvement

• Use Double#isNaN() to judge the result although it returns double type, it will not throw NFE when the result is NaN(0.0 / 0.0).
• Judge every place that use the double type in OSUtils and add Double#isNaN() judgement.