Add unit tests for ExternalAPIUtil

-Add unit tests for ExternalAPIUtil
-Add dependency injection via constructor
-Add factory for creating ExternalAPIUtil and RESTClient

Change-Id: Ied89afa3612de8d51424c95239341a57387ad94f
Issue-ID: SO-1195
Signed-off-by: Michal Kabaj <michal.kabaj@nokia.com>
diff --git a/pom.xml b/pom.xml
index e88d67f..1be848a 100644
--- a/pom.xml
+++ b/pom.xml
@@ -641,6 +641,7 @@
 		<dependency>
 			<groupId>org.assertj</groupId>
 			<artifactId>assertj-core</artifactId>
+			<version>3.11.1</version>
 			<scope>test</scope>
 		</dependency>
 		<dependency>