Fix make.conf WITH_PKGNG=yes content to handle \n

Using single quotes with \n will write this escape character into the
file, using double quotes will correctly write the newline into the
file.
Ensure /etc/make.conf file is present.

The file is required to be present in order for the file_line resource
to work correctly. Add require to ensure the file is created before the
WITH_PKGNG is attempted to be set.
Fix puppet-lint indentation for previous commit.
Merge pull request #9 from geoffgarside/make-conf

Ensure /etc/make.conf is present for file_line to work