daemon-utils: remove usage of here-docs

In some versions of bash, here-docs and here-strings use temporary
files, which means daemon-util needs a writable temporary filesystem.
Since echo is a bash builtin anyway, it's simple to switch to it and
remove this dependency.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Michael Hanselmann <hansmi@google.com>