do not install checkinstall package
do not install the build-essential metapackage, cherrypick what we want
switch to sameersbn/debian:jessie.20140918 baseimage
moved build dependency installation to the install script

the build dependency packages are removed at the end of the install as
they will not be required anymore.
replace `--no-ri --no-rdoc` with `--no-document` in the gem install command