avocado.utils.distro: Correctly identify CentOS 7.X

The current probe is not identifying the version numbers
for CentOS 7.X. Let's use a more relaxed regexp to fix
that problem.
Signed-off-by: NLucas Meneghel Rodrigues <lookkas@gmail.com>

avocado/utils/distro.py

@@ -315,7 +315,7 @@ class CentosProbe(RedHatProbe):
     CHECK_FILE = '/etc/redhat-release'
     CHECK_FILE_CONTAINS = 'CentOS'
     CHECK_FILE_DISTRO_NAME = 'centos'
-    CHECK_VERSION_REGEX = re.compile(r'CentOS release (\d{1,2})\.(\d{1,2}).*')
+    CHECK_VERSION_REGEX = re.compile(r'CentOS.* release (\d{1,2})\.(\d{1,2}).*')
 
 
 class FedoraProbe(RedHatProbe):