fixed duplicate port forwarding
removed get_vapp_port_forwarding_external_ports

function get_vapp_port_forwarding_external_ports no longer needed
corrected integer type in Set
removed duplication function poweron_vm
also check used ports in edge gateway
show also HTTP method in debug log
better variable names
removed edge_gateway_rules code from power_on
add_edge_gateway_rules for DNAT rule per port
removed set_edge_gateway_rules, no longer needed
added optional vapp_prefix to name the vapp
cache return value of get_vapp_edge_public_ip

cache return value of get_vapp_edge_public_ip to have vapp edge ip
address to remove all DNAT/SNAT edge gateway rules