Change issuegen to use #!/bin/bash due to bash-style echo usage

The \'s are always interpreted in dash/POSIX shell, issuegen expects
them to be ignored without -e.
Merge pull request #135 from vcaputo/issuegen_usebash

Change issuegen to use #!/bin/bash due to bash-style echo usage
Merge branch 'master' of https://github.com/coreos/init