qemurunner.py: replace 'codecs.open()' with 'open()'

qemurunner.py: replace 'codecs.open()' with 'open()'

With newer Python versions, codecs.open() is deprecated, leading to the
following warning:

|Stderr:
|/srv/pokybuild/tgamblin-qemux86/openembedded-core/meta/lib/oeqa/utils/qemurunner.py:133: DeprecationWarning: codecs.open() is deprecated. Use open() instead.
|  with codecs.open(self.logfile + extension, "ab") as f:

Note that if we try to be explicit and make the 'errors' keyword
'strict' (as the codecs.open() call defaulted to), we see other
warnings:

|ValueError: binary mode doesn't take an errors argument

Signed-off-by: Trevor Gamblin <tgamblin@baylibre.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>