test: skip cpu-intensive tests on slow hosts

The `test-tick-processor-*` tests are now passing everywhere except for
the single-processor 700MHz Raspberry Pi 1 devices.

The tests are CPU-intensive. Skip the tests if there is only one CPU and
it runs at a speed not more than 700 MHz.

PR-URL: https://github.com/nodejs/node/pull/8652


Reviewed-By: Matthew Loring <mattloring@google.com>