Fix ignored tests with missing external services

[IvanHdzC]

On PR #1892 Some tests were ignored for build

cygnus-common/src/test/java/com/telefonica/iot/cygnus/backends/kafka/KafkaBackendImplTest.java

and

cygnus-common/src/test/java/com/telefonica/iot/cygnus/utils/auth/keystone/KeyStoneUtilsTest.java

This is because those tests make calls to external services or modules outside Cygnus itself.

In order to enable them again, it's necessary to mock all conections and files necesary to work.