avocado.plugins.plugin_list: Update plugins lister to show failures loading plugins

Pick the information collected while loading plugins to display to the
user clearly why some of their plugins are not working.

Changes from v1:

* Instead of guessing the plugin disable cause, use a more generic but
  accurate description.  The description chosen is to simply say that
  the plugin was disabled during configuration (`configure()`), which
  is often done, but not limited to, missing dependencies.
* Changed the presentation from having colored `Enabled` or `Disabled`
  at the RHS of the plugin description to a single colored header.
* Increased one space in the formatting string (`format_str`)
Signed-off-by: NLucas Meneghel Rodrigues <lmr@redhat.com>
Signed-off-by: NCleber Rosa <crosa@redhat.com>

avocado/core/plugins/plugin_list.py

@@ -12,9 +12,10 @@
 # Copyright: Red Hat Inc. 2013-2014
 # Author: Ruda Moura <rmoura@redhat.com>
 
+from avocado.core import output
 from avocado.core.plugins import plugin
+from avocado.core.plugins.builtin import ErrorsLoading
 from avocado.core.plugins.manager import get_plugin_manager
-from avocado.core import output
 
 
 class PluginList(plugin.Plugin):
@@ -40,18 +41,34 @@ class PluginList(plugin.Plugin):
         view = output.View(app_args=args,
                            use_paginator=args.paginator == 'on')
         pm = get_plugin_manager()
-        view.notify(event='message', msg='Plugins loaded:')
+
+        enabled = [p for p in pm.plugins if p.enabled]
+        disabled = [p for p in pm.plugins if not p.enabled]
+
         blength = 0
         for plug in pm.plugins:
             clength = len(plug.name)
             if clength > blength:
                 blength = clength
+        for load_error in ErrorsLoading:
+            clength = len(load_error[0])
+            if clength > blength:
+                blength = clength
+        format_str = "    %-" + str(blength + 1) + "s %s"
+
+        if enabled:
+            view.notify(event='message', msg=output.term_support.healthy_str("Plugins enabled:"))
+            for plug in sorted(enabled):
+                view.notify(event='minor', msg=format_str % (plug.name, plug.description))
+
+        if disabled:
+            view.notify(event='message', msg=output.term_support.fail_header_str('Plugins disabled:'))
+            for plug in sorted(disabled):
+                view.notify(event='minor', msg=format_str % (plug.name, "Disabled during plugin configuration"))
+
+        if ErrorsLoading:
+            view.notify(event='message', msg=output.term_support.fail_header_str('Unloadable plugin modules:'))
+            for load_error in sorted(ErrorsLoading):
+                view.notify(event='minor', msg=format_str % (load_error[0], load_error[1]))
 
-        format_str = "    %-" + str(blength) + "s %s %s"
-        for plug in sorted(pm.plugins):
-            if plug.enabled:
-                status = "(Enabled)"
-            else:
-                status = "(Disabled)"
-            view.notify(event='minor', msg=format_str % (plug.name, plug.description, status))
         view.cleanup()