Enable QML_IMPORT_TRACE for setImportPathList and setPluginPathList

Enable QML_IMPORT_TRACE for setImportPathList and setPluginPathList

Currently QQmlImportDatabase methods addPluginPath and addImportPath
are providing a debug output by QML_IMPORT_TRACE environment variable.
QQmlImportDatabase::setImportPathList and QQmlImportDatabase - do not.
So the current import/plugin path list might be inconsistent with the
provided debug output.

This commit adds support for QML_IMPORT_TRACE for both 'set' methods.

Change-Id: I52bb3c7b7e7e5c1119f5b73c7574da2952f4242d
Reviewed-by: Matthew Vogt <matthew.vogt@nokia.com>