[ENHANCEMENT] Gather hardware information when creating instrumentation summaries

[benblank]

While analyzing the speed of slow builds, we found it handy to have a number of hardware and hardware-related statistics which may affect build speed available.

This adds the following fields to summary.platform within the instrumentation files produced when BROCCOLI_VIZ=1:

• isUsingBattery — true if the build host is running off battery power, false if it is not, or null if it cannot be determined.
• memorySwapUsed — The amount of swap memory currently used by the host, in bytes, or null if it cannot be determined.
• memoryTotal — The total amount of physical memory available on the build host.
• memoryUsed — The "Resident Set Size" reported by the Node process.
• processorCount — The number of logical processors on the build host.
• processorLoad — An array of three values representing the build host's processor load, over a 1-, 5-, and 15- minute range, or null if it cannot be determined.
• processorSpeed — The average speed of the build host's processor(s).

These changes have been tested on Node 6.17.1, 8.16.0, 10.15.3, and 11.14.0. The following platforms have also been tested:

• FreeBSD 12.0
• macOS 10.14
• OpenBSD 6.4
• RHEL 7
• Ubuntu 16.04
• Ubuntu 18.04
• Windows 7
• Windows 8.1
• Windows 10

[stefanpenner]

Hey @benblank I totally missed this PR, this is looking really good!

I notice this is still a draft, is some work remaining? Otherwise, to me this looks really good.

@rwjblue r?