Python 3: fix re.findall() using string pattern on a bytes-like object

re.findall(regexp, out) or re.search need regexp and out in the same type:st
currently regexp is string,but out is bytes,which cause exception thrown whe
Fix this issue by transfering out into string forcedly
Signed-off-by: Nchunfuwen <chwen@redhat.com>

avocado/utils/software_manager.py

@@ -408,7 +408,7 @@ class YumBackend(RpmBackend):
         y_cmd = executable + ' --version | head -1'
         cmd_result = process.run(y_cmd, ignore_status=True,
                                  verbose=False, shell=True)
-        out = cmd_result.stdout.strip()
+        out = cmd_result.stdout_text.strip()
         try:
             ver = re.findall(r'\d*.\d*.\d*', out)[0]
         except IndexError: