Improve Fedora support for boot-stack and openstack-db elements

- distro-specific DNS resolution configuration
- handle distro-specific location for the my.cnf file
- prevent from blindly running the apt-get command

Change-Id: I6f334913dedf5c3678fa8385226ee9c0c256a319
Merge "Improve Fedora support for boot-stack and openstack-db elements"