bitbake: toaster: use decode('utf-8') for binary data

Decoded binary data to utf-8 to fix the following
error when runnign on python 3:
TypeError: Type str doesn't support the buffer API

[YOCTO #9584]

(Bitbake rev: 752ea00919ef054622a51ce097923309934eff2b)

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

bitbake/lib/toaster/bldcontrol/localhostbecontroller.py

@@ -70,7 +70,7 @@ class LocalhostBEController(BuildEnvironmentController):
             raise ShellCmdException(err)
         else:
             logger.debug("localhostbecontroller: shellcmd success")
-            return out
+            return out.decode('utf-8')
 
     def getGitCloneDirectory(self, url, branch):
         """Construct unique clone directory name out of url and branch."""