CCT-10: Ensure IPv6-based URLs are properly formatted

* Card ID: CCT-10

Recent changes (e83e637) fixed parsing information from IPv6 URLs. This
patch fixes writing these addresses back as strings, mainly into
configuration files.

Previously, passing in IPv6 URL in e.g. `--baseurl` during registration
resulted in broken address in the config file:

$ subscription-manager register --baseurl https://[::1]:8443/prefix
$ cat /etc/rhsm/rhsm.conf | grep baseurl
baseurl=https://::1:8443/prefix

After this patch, the square brackets are written when port is
specified:

$ cat /etc/rhsm/rhsm.conf | grep baseurl
baseurl=https://[::1]:8443/prefix

Due to the state of the code, it is likely that this problem also exists
in other parts. If that is true, it is most likely in less sensitive
parts, such as during logging. Looking back, using `ipaddress` stdlib
would have been the right way to do this, but it is too late to do that.

src/subscription_manager/utils.py

@@ -117,6 +117,11 @@ def format_baseurl(hostname: str, port: str, prefix: str) -> str:
     if prefix == DEFAULT_CDN_PREFIX:
         prefix = prefix[:-1]
 
+    # Handle raw IPv6 addresses.
+    # RFC 1035 only allows characters `a-zA-Z0-9.`, we can do this.
+    if ":" in hostname:
+        hostname = f"[{hostname}]"
+
     # just so we match how we format this by
     # default
     if port == DEFAULT_CDN_PORT:

test/test_utils.py

@@ -290,6 +290,22 @@ def test_format_not_fqdn_with_port(self):
         self.assertEqual(prefix, DEFAULT_CDN_PREFIX)
         self.assertEqual("https://foo-bar:8088", format_baseurl(hostname, port, prefix))
 
+    def test_ipv4(self):
+        result = format_baseurl(hostname="127.0.0.1", port="8080", prefix="/foo")
+        self.assertEqual("https://127.0.0.1:8080/foo", result)
+
+    def test_ipv6(self):
+        result = format_baseurl(hostname="::1", port="8080", prefix="/foo")
+        self.assertEqual("https://[::1]:8080/foo", result)
+
+    def test_ipv6_default_port(self):
+        result = format_baseurl(hostname="::1", port="443", prefix="/foo")
+        self.assertEqual("https://[::1]/foo", result)
+
+    def test_ipv6_no_prefix(self):
+        result = format_baseurl(hostname="::1", port="8080", prefix="/")
+        self.assertEqual("https://[::1]:8080", result)
+
 
 class TestUrlBaseJoinEmptyBase(fixture.SubManFixture):
     def test_blank_base_blank_url(self):