fix: machines get should accept query params

[skatsaounis]

This PR contains all the filter options that can be set to MAAS v2 API to limit the machine list results.

The full list was gathered from source code:

• https://github.com/canonical/maas/blob/master/src/maasserver/api/machines.py#L1962
• https://github.com/canonical/maas/blob/master/src/maasserver/api/nodes.py#L807
• https://github.com/canonical/maas/blob/master/src/maasserver/node_constraint_filter_forms.py#L1356
• https://github.com/canonical/maas/blob/master/src/maasserver/node_constraint_filter_forms.py#L729

Fixes: #67

[jtoft-crusoe]

@skatsaounis Awesome work; I was just about to make a PR myself and saw you'd already tackled it.

Hopefully we can get this merged soon.

[skatsaounis]

This is an example of handpicked filter options that can limit the results:

params := entity.MachinesParams{
	ID:         []string{"qfkedy", "bdfsrr"},
	NotStatus:  []string{"ready"},
	Status:     []string{"deployed"},
	Hostname:   []string{"maas-host"},
	LinkSpeed:  []int{1000},
	MACAddress: []string{"12:34:56:ab:ce:12"},
	Storage:    "root:100(rotary)",
	Devices:    "commissioning_driver=virtio-pci,product_id=1041",
}
results, err := client.Machines.Get(&params)
if err != nil {
	fmt.Println(err)
}
fmt.Println(len(results))

[matthewconolly-lambda]

Thanks for doing this!!