Be systematic about parsing and validating hostnames and addresses

This adds a parse_address(pattern) utility function that returns
(host,port), and uses it wherever where we accept IPv4 and IPv6
addresses and hostnames (or host patterns): the inventory parser
the the add_host action plugin.

It also introduces a more extensive set of unit tests that supersedes
the old add_host unit tests (which didn't actually test add_host, but
only the parsing function).

test/units/parsing/test_addresses.py

@@ -0,0 +1,56 @@
+import unittest
+
+from ansible.parsing.utils.addresses import parse_address
+
+class TestParseAddress(unittest.TestCase):
+
+    tests = {
+        # IPv4 addresses
+        '192.0.2.3': ['192.0.2.3', None],
+        '192.0.2.3:23': ['192.0.2.3', 23],
+
+        # IPv6 addresses
+        '::': ['::', None],
+        '::1': ['::1', None],
+        '[::1]:442': ['::1', 442],
+        'abcd:ef98:7654:3210:abcd:ef98:7654:3210': ['abcd:ef98:7654:3210:abcd:ef98:7654:3210', None],
+        '[abcd:ef98:7654:3210:abcd:ef98:7654:3210]:42': ['abcd:ef98:7654:3210:abcd:ef98:7654:3210', 42],
+
+        # Hostnames
+        'some-host': ['some-host', None],
+        'some-host:80': ['some-host', 80],
+        'some.host.com:492': ['some.host.com', 492],
+        '[some.host.com]:493': ['some.host.com', 493],
+
+        # Various errors
+        '': [None, None],
+        'some..host': [None, None],
+        'some.': [None, None],
+        '[example.com]': [None, None],
+    }
+
+    range_tests = {
+        '192.0.2.[3:10]': ['192.0.2.[3:10]', None],
+        '192.0.2.[3:10]:23': ['192.0.2.[3:10]', 23],
+        'abcd:ef98::7654:[1:9]': ['abcd:ef98::7654:[1:9]', None],
+        '[abcd:ef98::7654:[6:32]]:2222': ['abcd:ef98::7654:[6:32]', 2222],
+        'foo[a:b]:42': ['foo[a:b]', 42],
+        'foo[a-b]:32': [None, None],
+        'foo[x-y]': [None, None],
+    }
+
+    def test_without_ranges(self):
+        for t in self.tests:
+            test = self.tests[t]
+
+            (host, port) = parse_address(t)
+            assert host == test[0]
+            assert port == test[1]
+
+    def test_with_ranges(self):
+        for t in self.range_tests:
+            test = self.range_tests[t]
+
+            (host, port) = parse_address(t, allow_ranges=True)
+            assert host == test[0]
+            assert port == test[1]