It might happen that user runs process with encoding that is ritcher
than system one. This is fine by the process as internally it stores
encoded bytes object, but the drainer might fail attempting to log the
output.

Those failures should not be critical as, under described circumstances,
the unavailability of the output is expected and should not prevent the
execution. Let's simply replace those characters using 'replace' (the
'xmlcharrefreplace' might fail with ASCII coder) and keep processing the
data.

To simplify error handling new "astring.to_text" argument "errors" is
added.
Signed-off-by: NLukáš Doktor <ldoktor@redhat.com>
Signed-off-by: NCleber Rosa <crosa@redhat.com>