add a parameter to change security_driver for qemu.conf

[rkhozinov]

The default security driver is SELinux. If SELinux is disabled on the host, then the security driver will automatically disable itself. If you wish to disable QEMU SELinux security driver while leaving SELinux enabled for the host in general, then set this to 'none' instead.
security_driver = "selinux"
qemu.conf.erb

[rkhozinov]

I've create the pull request #69

[asasfu]

I agree, this is a desired attribute, until a PR gets built to manage the conf files via hash so that we can alter multiple values without having service order issues when we need to modify more lines; it'd be nice to see this PR get merged. @igalic @thias
Thanks 😄