This patch adds gen-config tool which wraps oslo-config-generator.
It also moves README-higgins.conf.txt and
higgins-config-generator.conf files from etc/higgins to tools
directory so etc/higgins will only be used to maintain configuration
files of Higgins service.
Change-Id: I53cc5aeba6001b147c7cf6ffba33056470646f0f
d6e4831cb0