rename Csi to CSI to conform to Golang naming conventions
rename Csi to CSI to conform to Golang naming conventions

[#153830714](https://www.pivotaltracker.com/story/show/#153830714)

Signed-off-by: Kai Xiang <987005552a526059a0c9b4b70d166beabef8374e@pivotal.io>

cloudfoundry-incubator/volman,cloudfoundry-incubator/volman