generator: Use scion-pki tool

[oncilla]

Use scion-pki tool in the generator to have one way of generating
crypto material.

fixes #1491

---

This change is 

[lukedirtwalker]

Reviewed 6 of 6 files at r1.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @oncilla)

---

python/topology/cert.py, line 30 at r1 (raw file):

class CertGenerator(object):

Looks very clean now 💯

---

python/topology/config.py, line 270 at r1 (raw file):

                for path, value in cust_files[topo_id].items():
                    write_file(os.path.join(base, elem, path), value)
                    if self.args.cert_server == 'go':

This if would still be more or less relevant

[lukedirtwalker]

Reviewable status: all files reviewed, 2 unresolved discussions (waiting on @oncilla)

---

go/tools/scion-pki/internal/certs/cmd.go, line 100 at r1 (raw file):

var genCustomers = &cobra.Command{
	Use:   "customers",
	Short: "Collect customer keys",

Nit: genCustomers vs "Collect customer keys"

[oncilla]

Reviewable status: 4 of 6 files reviewed, 1 unresolved discussion (waiting on @lukedirtwalker)

---

go/tools/scion-pki/internal/certs/cmd.go, line 100 at r1 (raw file):

Previously, lukedirtwalker (Lukas Vogel) wrote…

Nit: genCustomers vs "Collect customer keys"

Done.

---

python/topology/config.py, line 270 at r1 (raw file):

Previously, lukedirtwalker (Lukas Vogel) wrote…

This if would still be more or less relevant

Done.

[lukedirtwalker]

Reviewed 2 of 2 files at r2.
Reviewable status: complete! all files reviewed, all discussions resolved