Refactor parsing of CLI args so that we can modify them in the base class

Implement tag and skip_tag handling in the CLI() class.  Change tag and
skip_tag command line options to be accepted multiple times on the CLI
and add them together rather than overwrite.

* Make it configurable whether to merge or overwrite multiple --tags arguments
* Make the base CLI class an abstractbaseclass so we can implement
  functionality in parse() but still make subclasses implement it.
* Deprecate the overwrite feature of --tags with a message that the
  default will change in 2.4 and go away in 2.5.

* Add documentation for merge_multiple_cli_flags
* Fix galaxy search so its tags argument does not conflict with generic tags
* Unit tests and more integration tests for tags

lib/ansible/cli/console.py

@@ -94,13 +94,12 @@ class ConsoleCLI(CLI, cmd.Cmd):
             help="one-step-at-a-time: confirm each task before running")
 
         self.parser.set_defaults(cwd='*')
-        self.options, self.args = self.parser.parse_args(self.args[1:])
+
+        super(AdHocCLI, self).parse()
 
         display.verbosity = self.options.verbosity
         self.validate_conflicts(runas_opts=True, vault_opts=True, fork_opts=True)
 
-        return True
-
     def get_names(self):
         return dir(self)