classes/lib: Update to use python3 command pipeline decoding

In python3, strings are unicode by default. We need to encode/decode
from command pipelines and other places where we interface with the
real world using the correct locales. This patch updates various
call sites to use the correct encoding/decodings.

(From OE-Core rev: bb4685af1bffe17b3aa92a6d21398f38a44ea874)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/lib/oeqa/runtime/ping.py

@@ -14,7 +14,7 @@ class PingTest(oeRuntimeTest):
         endtime = time.time() + 60
         while count < 5 and time.time() < endtime:
             proc = subprocess.Popen("ping -c 1 %s" % self.target.ip, shell=True, stdout=subprocess.PIPE)
-            output += proc.communicate()[0]
+            output += proc.communicate()[0].decode("utf-8")
             if proc.poll() == 0:
                 count += 1
             else: