selftests/functional/test_thirdparty_bugs.py: feed string to json

As it was done in d2b4edc3, Python 3.4 needs a string to be passed to
json.loads() (and, indirectly, to json.load()).  Different from
d2b4edc3, the content we fetch externally may be able to tell us the
encoding that is used.

Let's use that information, if available, to decode the stream of
bytes into a string that is acceptable to json.loads().
Signed-off-by: NCleber Rosa <crosa@redhat.com>

selftests/functional/test_thirdparty_bugs.py

+import re
 import json
 import unittest
 
@@ -9,6 +10,33 @@ except ImportError:
 from avocado.utils import download
 
 
+def get_content_by_encoding(url):
+    """
+    Returns the content of the given URL, attempting to use server provided
+    encoding.
+
+    :rtype: str
+    """
+    http_response = download.url_open(url)
+    content_type = None
+    encoding = None
+    if hasattr(http_response, 'headers'):
+        content_type = http_response.headers['Content-Type']
+    elif hasattr(http_response, 'getheader'):
+        content_type = http_response.getheader('Content-Type')
+    if content_type is not None:
+        match = re.match(r'^[az\\].*\; charset\=(.*)$', content_type)
+        if match is not None:
+            encoding = match.group(1)
+    content = http_response.read()
+    if hasattr(content, 'decode'):
+        if encoding is not None:
+            content = content.decode(encoding)
+        else:
+            content = content.decode()  # Python default encoding
+    return content
+
+
 class TestThirdPartyBugs(unittest.TestCase):
     """
     Class created to verify third-party known issues
@@ -20,7 +48,8 @@ class TestThirdPartyBugs(unittest.TestCase):
         # accepts RSA or DSS keys
         try:
             issue_url = 'https://api.github.com/repos/paramiko/paramiko/issues/243'
-            issue = json.load(download.url_open(issue_url))
+            content = get_content_by_encoding(issue_url)
+            issue = json.loads(content)
             self.assertEqual(issue['state'], 'open', 'The issue %s is not open '
                              'anymore. Please double check and, if already fixed, '
                              'change the avocado.conf option '
@@ -37,7 +66,8 @@ class TestThirdPartyBugs(unittest.TestCase):
         # on that file
         try:
             issue_url = 'https://api.github.com/repos/avocado-framework/inspektor/issues/31'
-            issue = json.load(download.url_open(issue_url))
+            content = get_content_by_encoding(issue_url)
+            issue = json.loads(content)
             self.assertEqual(issue['state'], 'open', 'The issue %s is not open '
                              'anymore. Please double check and, if already fixed, '
                              'remove the selftests/unit/test_utils_cpu.py from '