Bug#952879: [live-build] lack of robustness in echo helper output

[jnqnfe@gmail.com]

Package: live-build
Version: 1:20191221
Owner: jnqnfe@gmail.com

the echo helpers almost entirely do not explicitly direct their output
to stdout/stderr, and failing to do so means that in some use cases
(specifically use in functions whose purpose is to return a string (by
echoing it)) things go wrong with log messages (after all these after
effectively all logging functions) not making it to the console as they
should.

this could perhaps have been merged with #952878 which is specifically
about the error echo helper sending part of its output to stderr but
not all...

patch to be submitted via salsa shortly (will amend commit with bug
number first)