Run "make elpa" via "make before-test"

This completes 32538392ad7191b10a1653b1f6823063e9ee8691
Do not store install.log for "cask install"

... so that make notices exit status of "cask install".

This is to avoid error like this:
https://travis-ci.org/tkf/emacs-jedi/jobs/19448211#L493