(maint) Increase max-active-instances in thread test to 2
(maint) Increase max-active-instances in thread test to 2

In order to see multiple threads running concurrently through the
multithreaded JRuby pool, we need to allow more than one active instance
at a time. This commit updates the conf file for the thread test to use
allow two at a time.

puppetlabs/puppetserver,puppetlabs/puppet-server,puppetlabs/puppetserver,puppetlabs/puppetserver,puppetlabs/puppet-server,puppetlabs/puppetserver,puppetlabs/puppet-server