Add option to specify port of vSphere host

[andreasDalsgaard]

Add option to specify port of vSphere host. This makes it easy to test exporter in combination with vmware/vcsim, e.g.:

services:
  vcmock:
    image: vmware/vcsim
    ports:
      - "8989:8989"
  pryoda:
    image: pryorda_vmware_exporter_local
    environment:
      VSPHERE_USER: "user"
      VSPHERE_PASSWORD: "pass"
      VSPHERE_HOST: vcmock
      VSPHERE_PORT: 8989
      VSPHERE_SPECS_SIZE: "200"
      VSPHERE_IGNORE_SSL: "True"
    ports:
      - "9272:9272"