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.
