How to withdraw the WETH from the contract

The function would be something like this:

pragma solidity >=0.8.0;

function withdraw() {
    payable(msg.sender).transfer(address(this).balance);
}

Just make sure you only allow yourself to access it

I was able to deploy your FinalizableCrowdsale SampleCrowdsale after I removed the FinalizableCrowdsale() call from the constructor.

I used the following parameters in the constructor call:

1511030956, 1511117356, 1, 100, 200, "0x01", "0x02"

I deployed my contract using Remix, so I modified the code slightly to this (especially since I didn't have the TestToken code):

pragma solidity ^0.4.15;

import "github.com/OpenZeppelin/zeppelin-solidity/contracts/crowdsale/CappedCrowdsale.sol";
import "github.com/OpenZeppelin/zeppelin-solidity/contracts/crowdsale/FinalizableCrowdsale.sol";
import "github.com/OpenZeppelin/zeppelin-solidity/contracts/crowdsale/RefundableCrowdsale.sol";
import "github.com/OpenZeppelin/zeppelin-solidity/contracts/token/MintableToken.sol";

contract SampleCrowdsale is CappedCrowdsale, FinalizableCrowdsale {

    MintableToken public testToken ;

  function SampleCrowdsale(uint256 _startTime, uint256 _endTime, uint256 _rate, uint256 _goal, uint256 _cap, address _wallet, address _tokenContractAddress)
    CappedCrowdsale(_cap)
    Crowdsale(_startTime, _endTime, _rate, _wallet)
  {

    testToken = MintableToken(_tokenContractAddress);
  }

  function createTokenContract() internal returns (MintableToken) {
    return testToken;
  }

}

One thing that I noticed is that RefundableCrowdsale requires one argument for its constructor, where as FinalizableCrowdsale does not and it isn't necessary to call a parent's constructor if it doesn't take any arguments.

I suspect that this minor detail is the cause of the problem.