allow to provide user data for cloud testing VMs
FIX: usage() string in steering/run.sh
generic setup script can use curl instead of wget
run dummy sudo command for debugability
add contextualisation scripts for CentOS 7 x64
Merge pull request #569 from reneme/test-cc7

TEST: Integration Test Setup for CERN CentOS 7

This adapts the cloud testing system and adds contextualisation scripts for CERN CentOS 7. Besides the actual contextualisation scripts the VM steering infrastructure can now deal with userdata in order to pre-configure the CentOS image (i.e. disable requiretty in /etc/sudoers). Furthermore the CentOS image does not provide a pre-installed wget, thus the platform-independent installation script is now able to fall-back to curl.

Note: Currently there is no AUFS enabled kernel for CentOS 7, hence we can only run the client tests.