use here-documents and remove the need for the singlequotes parameter

We have some tests in forge that fail because of improper quoting of lines searched in files.

ValueError: invalid literal for int() with base 10: 'grep: lease: No such file or directory\ngrep: added. } \\]: No such file or directory\n0'

In this case, the lne itself contains double quotes and is enclosed in double quotes, so the result is, it splits the line into multiple parameters.

Instead of fixing each of them by quoting properly, I suggest we remove the need to quote by using here-documents (cat <<EOF, EOF).

This fixes some tests. And there are other changes that fix other tests.

Job: https://jenkins.aws.isc.org/view/Kea-manual/job/kea-manual/job/tarball-system-tests/223/