Add secure option for "Build an App"

[dianasaur323]

Current "Build a Test App" tutorial assumes insecure clusters. Add in an option for secure clusters.

conn = psycopg2.connect(database='bank',user='maxroach',host='localhost',port=26257, sslmode='require', sslrootcert='certs/ca.cert', sslcert='certs/maxroach.cert', sslkey='certs/maxroach.key')

[mberhault]

There are a few steps here, for each example:

• determine how the listed library accepts certs/keys. parameter names, file formats etc..
• when file formats differ, document how to convert our certs/keys to the expected format
• consider having the cockroach cert tools generate other formats.