doc: add note about key derivation

adds a note to the crypto docs passing along
the advice that openssl gives about what
key derivation function they recommend.

PR-URL: https://github.com/joyent/node/pull/8580
Reviewed-By: Fedor Indutny <fedor@indutny.com>
Merge remote-tracking branch 'joyent/v0.10' into v0.10
doc: update openssl commands to use best practices

This updates key size to 2048 and default hash function to sha256.

Reviewed-By: Fedor Indutny <fedor@indutny.com>
PR-URL: https://github.com/joyent/node/pull/8690
crypto: update CA bundle to latest from Mozilla

NOTE:

To reproduce/update this - run:

1. `perl tools/mk-ca-bundle.perl`
2. `node tools/rebuild-root-certs.js ca-bundle.crt > src/node_root_certs.h`
3. `rm ca-bundle.crt certdata.txt`

fix joyent/node#8679