qemu: fix qemu.conf security_driver
qemu: fix qemu.conf security_driver

Since a9331394 (first release v2.1.0), specifying a manual
security_driver setting in qemu.conf causes the daemon to fail to
start, erroring with 'Duplicate security driver X'.

The duplicate checking was incorrectly comparing every entry
against itself, guaranteeing a false positive.

https://bugzilla.redhat.com/show_bug.cgi?id=1365607

andreabolognani/libvirt,fabianfreyer/libvirt,jardasgit/libvirt,crobinso/libvirt,fabianfreyer/libvirt,nertpinx/libvirt,andreabolognani/libvirt,eskultety/libvirt,VenkatDatta/libvirt,libvirt/libvirt,libvirt/libvirt,jardasgit/libvirt,VenkatDatta/libvirt,VenkatDatta/libvirt,olafhering/libvirt,olafhering/libvirt,nertpinx/libvirt,eskultety/libvirt,taget/libvirt,andreabolognani/libvirt,fabianfreyer/libvirt,libvirt/libvirt,zippy2/libvirt,datto/libvirt,jfehlig/libvirt,crobinso/libvirt,eskultety/libvirt,datto/libvirt,taget/libvirt,fabianfreyer/libvirt,eskultety/libvirt,jfehlig/libvirt,nertpinx/libvirt,crobinso/libvirt,andreabolognani/libvirt,jfehlig/libvirt,taget/libvirt,libvirt/libvirt,jfehlig/libvirt,eskultety/libvirt,olafhering/libvirt,andreabolognani/libvirt,taget/libvirt,VenkatDatta/libvirt,zippy2/libvirt,datto/libvirt,jardasgit/libvirt,crobinso/libvirt,zippy2/libvirt,fabianfreyer/libvirt,taget/libvirt,jardasgit/libvirt,nertpinx/libvirt,zippy2/libvirt,datto/libvirt,datto/libvirt,olafhering/libvirt,jardasgit/libvirt,nertpinx/libvirt,VenkatDatta/libvirt