Fix unicorn pid auto-detection behavior

* run auto-detection on remote
* convert relative path to absolute
* use `unicorn -e` instead of `unicorn -c` with Tempfile
Revert deleting auto-detection failure log
Use app_path instead of current_path
Switch sudo to su -l
Merge branch 'fix-pid-auto-detection' of https://github.com/k2nr/capistrano-unicorn into capistrano3

Conflicts:
	lib/capistrano-unicorn/utility.rb