test: run tests even if os.cpus() fails

Currently if the os.cpus() call fails every test will fail. As there is
already a test for os.cpus(), the other tests should run even if the
os.cpus() call fails.

test/common.js

@@ -32,7 +32,8 @@ exports.isOSX = process.platform === 'darwin';
 exports.enoughTestMem = os.totalmem() > 0x40000000; /* 1 Gb */
 
 const cpus = os.cpus();
-exports.enoughTestCpu = cpus.length > 1 || cpus[0].speed > 999;
+exports.enoughTestCpu = Array.isArray(cpus) &&
+                        (cpus.length > 1 || cpus[0].speed > 999);
 
 exports.rootDir = exports.isWindows ? 'c:\\' : '/';
 exports.buildType = process.config.target_defaults.default_configuration;