salt-ssh: fix JSON load of return data when it contains non-ascii

For reasons I can't explain, in `salt.utils.json.find_json()` using
`.splitlines()` will sometimes convert a unicode string into a list of
str types on Python 2. So, that's weird. This can be triggered in
salt-ssh whenever there are non-ascii chars in the return data.

[DEBUG] raw = u'{"local": {"return": {"foo": "\xf6\xe4\xfc"}}}'
[DEBUG] raw.splitlines() = ['{"local": {"return": {"foo": "\xc3\xb6\xc3\xa4\xc3\xbc"}}}']

To resolve this, the UnicodeDecodeError is caught and reattempted with a
decoded list.

Additionally, this fixes a performance oversight. We process the string
one line at a time but we are iterating a number of times equal to the
length of the string. This means that we will nearly always end up doing
a bunch of extra list slices resulting in empty lists, which when joined
and loaded will produce ValueErrors, which we are catching and ignoring.
By enumerating over the split string, we ensure that we only iterate at
most a number of times equal to the amount of lines in the string.

salt/utils/json.py

@@ -25,8 +25,13 @@ def find_json(raw):
     string to start with garbage and end with json but be cleanly loaded
     '''
     ret = {}
-    for ind, _ in enumerate(raw):
-        working = '\n'.join(raw.splitlines()[ind:])
+    lines = raw.splitlines()
+    for ind, _ in enumerate(lines):
+        try:
+            working = '\n'.join(lines[ind:])
+        except UnicodeDecodeError:
+            working = '\n'.join(salt.utils.data.decode(lines[ind:]))
+
         try:
             ret = json.loads(working)  # future lint: blacklisted-function
         except ValueError: