Fix for SW-112:
- moteState component dispatches an infoDagRoot signal only when he mote switches to being a DAGroot.
- RPL module only registers when not registered yet. Unregisters from previous if dagroot changes
- eventBusClient break when finds callback
- small code cleanup
SW-112. Addressing suggestions from https://openwsn.atlassian.net/browse/SW-112?focusedCommentId=14501&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-14501.
SW-112. Don't send DIOs after unregister DAG root
Merge pull request #63 from kb2ma/develop_SW-112

SW-112. Don't send DIOs after unregister DAG root
Merge pull request #62 from openwsn-berkeley/develop_SW-112

Fix for SW-112: