Pin test-requirement for Nova to Havana

Change-Id: If5f28cf19211a69b4d2b6094ff05b6e82129d873
mongodb, db2: do not print full URL in logs

The full URL used to connect to MongoDB or DB2 might contains sensitive
information such as username and password, so it's better to not print
it at all.
Instead, just print the hosts that are being connected to.

Fixes-Bug: #1244476

(cherry picked from commit f2e651181f0016e96a123556aba46bd8d91e0012)

Change-Id: I4390020d24386df38b1fae32aeeb657456142abd