test: increase crypto strength for FIPS standard

Use stronger crypto (larger keys, etc.) for arbitrary tests so
they will pass in both FIPS and non-FIPS mode without altering
the original intent of the test cases.

PR-URL: https://github.com/nodejs/node/pull/3758


Reviewed-By: Shigeki Ohtsu <ohtsu@iij.ad.jp>
Reviewed-By: James M Snell <jasnell@gmail.com>