[calamares] Better config-loading diagnostics

- Be more verbose when things go wrong while loading module-
   configuration files.
 - Allow more forms of paths to be specified. In debug mode, this
   is mostyle helpful for the module test-loader.

src/libcalamaresui/modulesystem/Module.cpp

@@ -145,8 +145,15 @@ moduleConfigurationCandidates( bool assumeBuildDir, const QString& moduleName, c
         paths << CalamaresUtils::appDataDir().absoluteFilePath( QString( "modules/%1" ).arg( configFileName ) );
     else
     {
+        // If an absolute path is given, in debug mode, look for it
+        // first. The case contains('/'), below, will add the absolute
+        // path a second time, though.
+        if ( assumeBuildDir && configFileName.startsWith( '/' ) )
+            paths << configFileName;
         if ( assumeBuildDir )
             paths << QDir().absoluteFilePath(QString( "src/modules/%1/%2" ).arg( moduleName ).arg( configFileName ) );
+        if ( assumeBuildDir && configFileName.contains( '/' ) )
+            paths << QDir().absoluteFilePath( configFileName );
 
         paths << QString( "/etc/calamares/modules/%1" ).arg( configFileName );
         paths << CalamaresUtils::appDataDir().absoluteFilePath( QString( "modules/%1" ).arg( configFileName ) );
@@ -168,6 +175,7 @@ Module::loadConfigurationFile( const QString& configFileName ) //throws YAML::Ex
             YAML::Node doc = YAML::Load( ba.constData() );
             if ( doc.IsNull() )
             {
+                cDebug() << "Found empty module configuration" << path;
                 // Special case: empty config files are valid,
                 // but aren't a map.
                 return;
@@ -178,14 +186,13 @@ Module::loadConfigurationFile( const QString& configFileName ) //throws YAML::Ex
                 return;
             }
 
+            cDebug() << "Loaded module configuration" << path;
             m_configurationMap = CalamaresUtils::yamlMapToVariant( doc ).toMap();
             m_emergency = m_maybe_emergency
                           && m_configurationMap.contains( EMERGENCY )
                           && m_configurationMap[ EMERGENCY ].toBool();
             return;
         }
-        else
-            continue;
     }
 }