Add CentOS-specific OpenSSL package installation.

Add openssl-devel package installation procedure to tools/install_venv.py
It fixes CentOS-specific package dependency. pip install pyOpenSSL
will work well after installing openssl-devel package.

Change-Id: Ia8c5cdd48260996e33b752ccb956c9e072a8f3d8
Merge "Add CentOS-specific OpenSSL package installation."