SquishTests: Handle codec problems

Reading files depends on the system encoding and will
return a bytes object instead of a str even for text files
on some Windows setups.
Handle this by explcitly converting to str if needed.
Handle possible decoding issues by falling back to UTF8
encoding when running into decoding error while decoding
on Windows.

Change-Id: I8c1f24ff052710e4b1927399d54e321088e3b171
Reviewed-by: Marcus Tillmanns <marcus.tillmanns@qt.io>

tests/system/shared/utils.py

@@ -611,8 +611,12 @@ def stringify(obj):
     if isinstance(obj, stringTypes):
         return obj
     if isinstance(obj, bytes):
-        tmp = obj.decode('cp1252') if platform.system() in ('Microsoft','Windows') else obj.decode()
-        return tmp
+        if not platform.system() in ('Microsoft', 'Windows'):
+            return obj.decode()
+        try:
+            return obj.decode('cp1252')
+        except UnicodeDecodeError:
+            return obj.decode('utf-8')
 
 
 class GitClone:

tests/system/suite_editors/tst_edit_externally/test.py

@@ -39,7 +39,10 @@ def main():
             test.fatal("Could not get the editor for '%s'" % currentFile,
                        "Skipping this file for now.")
             continue
+
         contentBefore = readFile(currentFile)
+        if not currentFile.endswith(".bin"):
+            contentBefore = stringify(contentBefore)
         if i % 2 == 0:
             # modify current file and store content for next modification
             formerContent = contentBefore