Added new 'iso_installer' task.

Added new 'iso_installer' task and refactored code that enables RHEL
repositories for Satellite 7 installations.
Merge pull request #24 from omaciel/install-from-iso

Added new 'iso_installer' task.
Better interface parsing for setup_default_capsule

This will ensure to use only one interface when parsing machine's
interfaces on setup_default_capsule task.
Don't setup default capsule for nightly install
Better naming for vm_destroy task arguments