Fix the position of color legend in Cloud UI.

This patch contains two display enhancements which make the legend easier to read, especially when the number of solr nodes is larger than 40.

1. In the Could -> Graph page,
   it difficult to read the server name and legend since they are overlapping. 
   (Page.1)
2.  In the Could -> Graph (Radial) page,
   the horizontal distance between the graph and the legend is too far.
   (Page.2)

These issues have been adjusted for a long time. 
Ref: https://issues.apache.org/jira/browse/SOLR-3915?focusedCommentId=13472876&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-13472876
And this patch provided a solution only modifying the cloud.css. The legend was moved to the outside of the graph so that it will keep at left-bottom corner without overlapping. (Page.3-4)