kvm: direct download templates for system VM (apache#134)

* kvm: direct download templates for system VM

System VMs now support direct download templates.
Different direct download timeouts have been made configurable with new global settings.

Signed-off-by: Abhishek Kumar <abhishek.mrt22@gmail.com>

* suggestion applied

Co-authored-by: Andrija Panic <45762285+andrijapanicsb@users.noreply.github.com>

Co-authored-by: Andrija Panic <45762285+andrijapanicsb@users.noreply.github.com>

vsphere 6.7u3-u3f crash notice (apache#130)

* Update compat.rst

* Update compat.rst

add note on firewall for integration.api.port 8096

Signed-off-by: Rohit Yadav <rohit.yadav@shapeblue.com>

Updated documentation for 4.12.0.0 release