Fixed prepare.sh and other small fixes

List of fixes:
- Use -g option to set ext gw info for heat-router in prepare.sh
- Fixed -H option in prepare.sh
- Fixed default working directory in prepare.sh
- Use admin_username from env vars in prepare.sh
- Set additional quotas for cvp.project
- Use mirantis busybox image from mirantis registry
- Fixed FIXED_NET variable in rally templates

Related-PROD: PROD-37187
Change-Id: I3d3ea6a520cf1677aabfa356bc40c19ae04822b4
5 files changed