scripts: Fix encoding errors for python3

Moved call of decode('utf-8') as close as possible to
call of subprocess API to avoid calling it in a lot of
other places.

Decoded binary data to utf-8 where appropriate to fix devtool
and recipetool tests in python 3 environment.

(From OE-Core rev: 30d02e2aa2d42fdf76271234b2dc9f37bc46b250)

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

meta/lib/oe/patch.py

@@ -292,7 +292,10 @@ class GitApplyTree(PatchTree):
     def decodeAuthor(line):
         from email.header import decode_header
         authorval = line.split(':', 1)[1].strip().replace('"', '')
-        return decode_header(authorval)[0][0]
+        result =  decode_header(authorval)[0][0]
+        if hasattr(result, 'decode'):
+            result = result.decode('utf-8')
+        return result
 
     @staticmethod
     def interpretPatchHeader(headerlines):