spec: Disable libssh2 support for RHEL
spec: Disable libssh2 support for RHEL

https://bugzilla.redhat.com/show_bug.cgi?id=905513

Libssh2 isn't reliable enough to support the libvirt transport using it.
The problems include mishandling of "known_hosts" files that may confuse
users.

VenkatDatta/libvirt,datto/libvirt,eskultety/libvirt,jfehlig/libvirt,andreabolognani/libvirt,rlaager/libvirt,libvirt/libvirt,rlaager/libvirt,elmarco/libvirt,zhlcindy/libvirt-1.1.4-maintain,zhlcindy/libvirt-1.1.4-maintain,nertpinx/libvirt,shugaoye/libvirt,cbosdo/libvirt,zhlcindy/libvirt-1.1.4-maintain,fabianfreyer/libvirt,olafhering/libvirt,olafhering/libvirt,taget/libvirt,eskultety/libvirt,fabianfreyer/libvirt,VenkatDatta/libvirt,datto/libvirt,elmarco/libvirt,jardasgit/libvirt,jfehlig/libvirt,VenkatDatta/libvirt,jfehlig/libvirt,crobinso/libvirt,eskultety/libvirt,jardasgit/libvirt,crobinso/libvirt,taget/libvirt,andreabolognani/libvirt,cbosdo/libvirt,agx/libvirt,agx/libvirt,andreabolognani/libvirt,shugaoye/libvirt,cbosdo/libvirt,nertpinx/libvirt,libvirt/libvirt,jardasgit/libvirt,fabianfreyer/libvirt,zippy2/libvirt,agx/libvirt,fabianfreyer/libvirt,elmarco/libvirt,taget/libvirt,rlaager/libvirt,VenkatDatta/libvirt,andreabolognani/libvirt,jardasgit/libvirt,andreabolognani/libvirt,fabianfreyer/libvirt,eskultety/libvirt,jardasgit/libvirt,crobinso/libvirt,elmarco/libvirt,libvirt/libvirt,jfehlig/libvirt,datto/libvirt,shugaoye/libvirt,crobinso/libvirt,cbosdo/libvirt,eskultety/libvirt,libvirt/libvirt,zippy2/libvirt,rlaager/libvirt,zhlcindy/libvirt-1.1.4-maintain,datto/libvirt,nertpinx/libvirt,taget/libvirt,agx/libvirt,zippy2/libvirt,zhlcindy/libvirt-1.1.4-maintain,rlaager/libvirt,VenkatDatta/libvirt,elmarco/libvirt,cbosdo/libvirt,nertpinx/libvirt,shugaoye/libvirt,taget/libvirt,zippy2/libvirt,agx/libvirt,olafhering/libvirt,nertpinx/libvirt,datto/libvirt,olafhering/libvirt,shugaoye/libvirt