qemurunner.py: ignore decode errors

qemurunner.py: ignore decode errors

qemu output can contain control characters. This cause qemurunner
API to crash when decoding the output to utf-8:

Traceback (most recent call last):
  File "/usr/lib64/python3.4/threading.py", line 911, in _bootstrap_inner
    self.run()
  File "meta/lib/oeqa/utils/qemurunner.py", line 472, in run
    threading.Thread.run(self)
  File "/usr/lib64/python3.4/threading.py", line 859, in run
    self._target(*self._args, **self._kwargs)
  File "meta/lib/oeqa/utils/qemurunner.py", line 465, in threadtarget
    self.eventloop()
  File "meta/lib/oeqa/utils/qemurunner.py", line 526, in eventloop
    self.logfunc(data)
  File "meta/lib/oeqa/utils/qemurunner.py", line 77, in log
    msg = msg.decode("utf-8")
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xda in position 0:
unexpected end of data

Added errors='ignore' to decode call to fix this.

(From OE-Core rev: 4a46dd5190d97fdcb6297a0c1d8c824d425c4c51)

Signed-off-by: Ed Bartosh <ed.bartosh@linux.intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>