avocado.plugins: Add config plugin

Add the config plugin, that introduces the 'config'
subcommand. This shows to the user the config keys
available in the system.
Signed-off-by: NLucas Meneghel Rodrigues <lmr@redhat.com>

avocado/plugins/config.py

+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+#
+# See LICENSE for more details.
+#
+# Copyright: Red Hat Inc. 2013-2014
+# Author: Lucas Meneghel Rodrigues <lmr@redhat.com>
+
+from avocado.core import output
+from avocado.core import data_dir
+from avocado.settings import settings
+from avocado.plugins import plugin
+
+
+class ConfigOptions(plugin.Plugin):
+
+    """
+    Implements the avocado 'config' subcommand
+    """
+
+    name = 'config'
+    enabled = True
+
+    def configure(self, parser):
+        self.parser = parser.subcommands.add_parser(
+            'config',
+            help='Shows avocado config keys')
+        self.parser.add_argument('--datadir', action='store_true', default=False,
+                                 help='Shows the data directories currently being used by avocado')
+        super(ConfigOptions, self).configure(self.parser)
+
+    def run(self, args):
+        view = output.View()
+        view.notify(event="message", msg='Config file path: %s' % settings.config_path)
+        view.notify(event="minor", msg='')
+        if not args.datadir:
+            blength = 0
+            for section in settings.config.sections():
+                for value in settings.config.items(section):
+                    clength = len('%s.%s' % (section, value[0]))
+                    if clength > blength:
+                        blength = clength
+
+            format_str = "    %-" + str(blength) + "s %s"
+
+            view.notify(event="minor", msg=format_str % ('Section.Key', 'Value'))
+            for section in settings.config.sections():
+                for value in settings.config.items(section):
+                    config_key = ".".join((section, value[0]))
+                    view.notify(event="minor", msg=format_str % (config_key, value[1]))
+        else:
+            view.notify(event="minor", msg="Avocado replaces config dirs that can't be accessed")
+            view.notify(event="minor", msg="with sensible defaults. Please edit your local config")
+            view.notify(event="minor", msg="file to customize values")
+            view.notify(event="message", msg='')
+            view.notify(event="message", msg='Avocado Data Directories:')
+            view.notify(event="minor", msg='    base  ' + data_dir.get_base_dir())
+            view.notify(event="minor", msg='    tests ' + data_dir.get_test_dir())
+            view.notify(event="minor", msg='    data  ' + data_dir.get_data_dir())
+            view.notify(event="minor", msg='    logs  ' + data_dir.get_logs_dir())
+            view.notify(event="minor", msg='    tmp   ' + data_dir.get_tmp_dir())