openssl-devel needed for CentOS 6.3

In tools/install-venv.py, pip install pyOpenSSL doesn't work until installing openssl-devel package.

git diff
diff --git a/tools/install_venv.py b/tools/install_venv.py
index 42ed32c..0481013 100644
--- a/tools/install_venv.py
+++ b/tools/install_venv.py
@@ -95,9 +95,9 @@ class Distro(object):

 class Fedora(Distro):
- """This covers all Fedora-based distributions.
+ """This covers all Fedora-based distributions except CentOS.

- Includes: Fedora, RHEL, CentOS, Scientific Linux"""
+ Includes: Fedora, RHEL, Scientific Linux"""

     def check_pkg(self, pkg):
         return run_command_with_code(['rpm', '-q', pkg],
@@ -141,10 +141,21 @@ class Fedora(Distro):
                          'contrib/redhat-eventlet.patch')

+class CentOS(Fedora):
+ """This covers CentOS. """
+
+ def post_process(self):
+ if not self.check_pkg('openssl-devel'):
+ self.yum_install('openssl-devel', check_exit_code=False)
+
+
 def get_distro():
     if (os.path.exists('/etc/fedora-release') or
         os.path.exists('/etc/redhat-release')):
- return Fedora()
+ if os.path.exists('/etc/redhat-release') and run_command_with_code(['grep', 'CentOS', '/etc/redhat-release']) == 0:
+ return CentOS()
+ else:
+ return Fedora()
     else:
         return Distro()