Implement interruptible sleep and condition variable waitFor methods on OperationContext

SERVER-21004 introduced interruptible condition variable wait functions using OperationContext. This task is to also implement interruptible unconditional sleep methods and to round out the set of interruptible condition variable waits available, to more closely match those available on std::condition_variable.

To be implemented, at least:

OperationContext::sleepUntil()
OperationContext::sleepFor()
Various forms of OperationContext::waitForConditionOrInterruptFor.