Have you also added the xmltooling and openws dependencies to your POM file from the repository:
https://build.shibboleth.net/nexus/content/repositories/releases/org/opensaml/
<dependency>
<groupId>org.opensaml</groupId>
<artifactId>xmltooling</artifactId>
<version>1.3.2</version>
</dependency>
<dependency>
<groupId>org.opensaml</groupId>
<artifactId>openws</artifactId>
<version>1.4.2</version>
</dependency>
The xmltooling should have the xerces xml-api that is missing.
Thanks, Yogesh