oeqa/utils/qemurunner: fix logging

oeqa/utils/qemurunner: fix logging

OE-Core commit 519e381278d40bdac79add340e4c0460a9f97e17 unfortunately
broke logging in two different ways:

1) it prevented logging to the task log from working within bitbake
   -c testimage. This is due to the logger object being set up too early
   which interferes with BitBake's own logging. If we prefix the name
   with "BitBake." everything works (and we don't need to set the
   logging level).

2) Additionally because it called the log functions on the logging
   module and not the logger object it set up, this caused the
   oe-selftest logging to start printing everything from that point
   forward.

Fix these two issues and return us to the desired behaviour for
do_testimage.

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>