remove headless gem which was used by ui test earlier

Signed-off-by: Henry Chen <hchen@vmware.com>
Merge pull request #142 from Henry-CF/headless

remove headless gem which was used by ui test earlier
add rake to Gemfile

Signed-off-by: Henry Chen <hchen@vmware.com>
Merge pull request #143 from Henry-CF/rake

add rake to Gemfile