[TC-426] Postinstall -- answering "no" to certificate generation does not skip

[limited]

Answering 'no' to 'Do you want to generate a certificate?:' forces certificate generation. That section should have been skipped.

===========/opt/traffic_ops/install/data/json/openssl_configuration.json===========
Do you want to generate a certificate?: no
Country Name (2 letter code): US

Author: Dewayne Richardson
JIRA Link: https://issues.apache.org/jira/browse/TC-426
Found Version: 2.1.0

[dewrich]

Looks like this line fixes this issue now: https://github.com/apache/trafficcontrol/blob/master/traffic_ops/install/bin/_postinstall#L682