Do not mark python plugins as broken in plugin installer when having dash in the name

Although plugin with a dash in the name is not a correct python package name,
the qgis python support recognizes them as valid plugins - so let's have the same
behavior in the installer.

Author: wonder-sk

python/pyplugin_installer/installer_data.py

@@ -618,9 +618,9 @@ def pluginMetadata(fct):
       elif testLoad:
         # only testLoad if compatible version
         try:
-          exec "import %s" % key in globals(), locals()
-          exec "reload (%s)" % key in globals(), locals()
-          exec "%s.classFactory(iface)" % key in globals(), locals()
+          pkg = __import__(key)
+          reload(pkg)
+          pkg.classFactory(iface)
         except Exception, e:
           error = "broken"
           errorDetails = unicode(e.args[0])