Adding Missing EC2 Exceptions.

This PR adds EC2 exceptions that can be thrown when deploying an instance through the Ec2Client but were never implemented. Without these you basically end up with a lot of `fatal error: failed to open stream SomeEc2Exception` whenever something goes wrong when you try to bring up an instance in the Ec2Client. There might be more missing implementations but those were the ones identified during our internal testing.

If the downloadable SDK (composer independent) is used these exceptions also need to be added to the mapping in aws-autoloader.php:

```
    'Aws\Ec2\Exception\Ec2Exception' => __DIR__ . '/Aws/Ec2/Exception/Ec2Exception.php',
    'Aws\Ec2\Exception\InvalidParameterException' => __DIR__ . '/Aws/Ec2/Exception/InvalidParameterException.php',
    'Aws\Ec2\Exception\InvalidParameterValueException' => __DIR__ . '/Aws/Ec2/Exception/InvalidParameterValueException.php',
    'Aws\Ec2\Exception\InvalidAMIIDMalformedException' => __DIR__ . '/Aws/Ec2/Exception/InvalidAMIIDMalformedException.php',
    'Aws\Ec2\Exception\InvalidKeyPairNotFoundException' => __DIR__ . '/Aws/Ec2/Exception/InvalidKeyPairNotFoundException.php',
    'Aws\Ec2\Exception\InvalidSubnetIDNotFoundException' => __DIR__ . '/Aws/Ec2/Exception/InvalidSubnetIDNotFoundException.php',
    'Aws\Ec2\Exception\InvalidIPAddressInUseException' => __DIR__ . '/Aws/Ec2/Exception/InvalidIPAddressInUseException.php',
    'Aws\Ec2\Exception\InvalidParameterCombinationException' => __DIR__ . '/Aws/Ec2/Exception/InvalidParameterCombinationException.php',
    'Aws\Ec2\Exception\IncorrectStateException' => __DIR__ . '/Aws/Ec2/Exception/IncorrectStateException.php',
    'Aws\Ec2\Exception\InvalidInstanceIDNotFoundException' => __DIR__ . '/Aws/Ec2/Exception/InvalidInstanceIDNotFoundException.php',
    'Aws\Ec2\Exception\AuthFailureException' => __DIR__ . '/Aws/Ec2/Exception/AuthFailureException.php',
    'Aws\Ec2\Exception\InvalidBlockDeviceMappingException' => __DIR__ . '/Aws/Ec2/Exception/InvalidBlockDeviceMappingException.php',
    'Aws\Ec2\Exception\InsufficientInstanceCapacityException' => __DIR__ . '/Aws/Ec2/Exception/InsufficientInstanceCapacityException.php',
    'Aws\Ec2\Exception\InvalidSnapshotIDNotFoundException' => __DIR__ . '/Aws/Ec2/Exception/InvalidSnapshotIDNotFoundException.php',
```