Adds ability to change every word to attack loop.
Adds ability to change every word to attack loop.

If the number of tokens to change per sentence is 0, this allows
the attack loop to change every single word in the input. Previously
the number of tokens to change had to be specified so the only way
to change all tokens was to pick a very large number.

Change-Id: I61971c191afa1c8a8ebf1077ec6d6715abe41df6

googleinterns/adversarial-0th-order-optimization