Dynamically generate template parameters for different distros

We define hard coded template for different distros. It's not
flexible to generate templates for other platforms or new distros.

This patch changes to dynamically generate vm template. With
this change, it can support new distro, like Fedora20, without any
modifications.

Signed-off-by: Mark Wu <wudxw@linux.vnet.ibm.com>
Support VM template for Power machine

VM on power machine requires different parameters from X86 machine.
So kimchi should provide different template according to the architecture.
IDE bus is not available on power platform. So change the device
bus of cdrom to scsi instead of ide for VM on power. The same
problem exists for old nic model, and change it to rtl8139 instead.

Signed-off-by: Mark Wu <wudxw@linux.vnet.ibm.com>