Multiarch testcloud, artemis provision, test export improvements...

• Add multiarch support to testcloud provision
• Consistent summary for test export --nitrate
• Allow dry mode for tests export --nitrate
• Add a nice provisioning progress to Artemis plugin
• Add support for the where keyword to execute
• Adjust support for export of multiple tests
• Add support for exporting multiple tests
• Basic multihost test for the httpd web server
• Update multihost specification with guest groups
• Add a provision plugin for Artemis
• Fix exclude option in fmf discover
• Reduce the number of execute calls for reboot
• Add support for reboot in interactive mode