I found a solution to this. After the plugin gets installed, I go to .forge\plugins\org\switchyard\switchyard-forge-plugin\dependencies\0.3.0-SNAPSHOT-3b42bae9-11c7-4278-a698-6460cf84bc98 (my plugins's path) and edit the module.xml file.
I add this code inside the dependencies tag
<module name="org.jboss.forge.shell-api" services="import" optional="false">
<imports>
<include path="**" />
<include path="META-INF" />
</imports>
</module>
Then I can start forge normally.
Hope this is useful to someone...