fix #8488: added tests

Tests added for the implementation of _eval_is_prime in Mul class
fix #8488: added more tests
Better patch for fix to #8488

More complete implementation of _eval_is_prime for Mul class in core
module.

Example:
>>>Mul(4, S.Half, evaluate=False).is_prime
False
>>>Mul(sqrt(3), sqrt(3), evaluate=False).is_prime
True
>>>Mul(3, S.One, evaluate=False).is_prime
True
>>>k = Symbol('k', integer=True)
>>>(9*k).is_prime
False