gen_install_parameters() had contradictory logic: the outer guard
required all three arguments to be non-None/non-empty (making them
mutually inclusive), while the inner checks then treated each one
as optional.
Make each parameter independently optional (defaulting to None) and
remove the all-or-nothing guard from both the function and its caller.
Simplify the function body to a straightforward single-pass
construction of system_specific_params.
Change-Id: I8756fb38016cdf0527fe2e21edb44381d1dc557f
9aeac8f5df