refs #10777 Use sha256 as default signing algorithm.

[rojspencer]

sha1 has been deprecated by many browsers and throws warnings when the
certificate expires after 12/31/2016.

sha256 should be good for awhile.

[ehelms]

Did you have a test scenario to verify the change produces what you expect?

[rojspencer]

I ran the following to confirm the signature algorithm:

openssl x509 -text -noout -in /path/to/certificate.crt

and looked for the "Signature Algorithm:" line to contain sha256WithRSAEncryption

Suppose an automated test could do something like

if ! openssl x509 -text -noout -in /path/to/certificate.crt | grep -q sha256WithRSAEncryption; then
   echo "Fail: Certificate not signed with sha256 algorithm"
fi

[ehelms]

@rojspencer I will test this and merge/build to go out in nightly and 2.2 if all is well.

[ehelms]

Tested and works, thanks @rojspencer !