The existing sample functions miss the parameter `seed`, however, the corresponding function interface in `generics` has such a parameter. Thus, although the function caller can call the function with the 'seed', we are not using the value.

This could cause SparkR unit tests failed. For example, I hit it in another PR:
https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder/47213/consoleFull

Author: gatorsmile <gatorsmile@gmail.com>

Closes #10160 from gatorsmile/sampleR.