Changes

param_source: allow input val expansion like '0 * 32'

Working with keys, we often generate 4, 8, 16, 32 digit wide random
values. Those then typically have default input values like

 00000000000000000000000000000000

it is hard for humans to count the number of digits. Much easier:

 00*16

Teach the ParamSource subclasses dealing with random values to
understand an expansion like this. Any expansion is carried out before
all other input value handling.

Use this expansion also in the default_value of ConfigurableParameter
subclasses that have a default_source pointing at a ParamSource that now
understand this expansion.

Related: SYS#6768
Change-Id: Ie7171c152a7b478736f8825050305606b5af5735