After a careful reading https://community.jboss.org/message/626315#626315 and https://community.jboss.org/thread/219118 and https://docs.jboss.org/author/display/AS71/Class+Loading+in+AS7 I was able to fix the issue above by modifying the jboss-deployment-structure.xml on the EAR file as well as the jboss-deployment-structure.xml on the RAR.
The contents of the jboss-deployment-structure.xml file on the RAR (sevensys-cloud-adapter-aws.rar):
<?xml version="1.0" encoding="UTF-8"?>
<jboss-deployment-structure>
<deployment>
<exports>
<include path="mx/sevensys/cloud/api**" />
<include path="org/jclouds**" />
</exports>
<dependencies>
<module name="javax.inject.api"/>
<module name="javax.ws.rs.api"/>
<module name="javax.annotation.api"/>
</dependencies>
</deployment>
</jboss-deployment-structure>
The contents of the jboss-deployment-structure.xml file on the EAR:
<?xml version="1.0" encoding="UTF-8"?>
<jboss-deployment-structure>
<ear-subdeployments-isolated>false</ear-subdeployments-isolated>
<sub-deployment name="sample-ear-ejb.jar">
<dependencies>
<module name="deployment.sevensys-cloud-adapter-aws.rar"/>
</dependencies>
</sub-deployment>
</jboss-deployment-structure>