Pin puppetdb to 2.x

As we discovered in the course of upgrading puppetboard the puppetdb
package is upgraded independently of the puppetdb-terminus package,
but in fact it will break if they don't match. We now pin them to
the same values for safety.

Change-Id: I628129997e084ec5e4cb18947fa7e2362c9b4ba5
Merge "Pin puppetdb to 2.x"