Reuse validate_instance_and_node() Nova ironic Driver

The driver already counts with a function called
validate_instance_and_node() that checks which node is associated to
a given instance and raises InstanceNotFound if the instance UUID is
not found in Ironic. The same functionality was being duplicate in many
other parts of the driver, this patch simply update those parts to use
the validate_instance_and_node() function.

Change-Id: I9a2f90c7cdd0fdfcc00d49a49581c61e4f073888
Factoring out PXE and TFTP functions

Multiple drivers need to support neutron and Ironic's PXE and TFTP
server. Factoring them out into a common file will make that
transition possible. This moves all the generic calls into neutron
and reconfigures the PXE driver to work with the new functions.

Change-Id: I181ffabe673636b628329592e623e6425da54d6d
VendorPassthru.validate()s call _parse_driver_info

ipmitool's and seamicro's VendorPassthru methods use the parameters that
their _parse_driver_info() validates. Yet their VendorPassthru.validate()'s
weren't calling _parse_driver_info() to make sure that needed parameters
were specified/valid.

ipmitool's and seamicro's VendorPassthru.validate()s now call
 _parse_driver_info().

Change-Id: Ic6196bcc13024b914c04d35868f3d5f10e73f420
Closes-Bug: #1312383
Merge "Reuse validate_instance_and_node() Nova ironic Driver"
Merge "VendorPassthru.validate()s call _parse_driver_info"
Merge "Factoring out PXE and TFTP functions"