basevm: Call logging.basicConfig()

basevm: Call logging.basicConfig()

Just setting level=DEBUG when debug is enabled is not enough: we
need to set up a log handler if we want debug messages generated
using logging.getLogger(...).debug() to be printed.

This was not a problem before because logging.debug() calls
logging.basicConfig() implicitly, but it's safer to not rely on
that.

Cc: "Alex Bennée" <alex.bennee@linaro.org>
Cc: Fam Zheng <famz@redhat.com>
Cc: "Philippe Mathieu-Daudé" <f4bug@amsat.org>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Message-Id: <20170927130339.21444-4-ehabkost@redhat.com>
Reviewed-by: Daniel P. Berrange <berrange@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Lukáš Doktor <ldoktor@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>