Changed os::sleep() to take a Duration instead of a double.

From: Jiang Yan Xu <yan@jxu.me>
Review: https://reviews.apache.org/r/10231

git-svn-id: https://svn.apache.org/repos/asf/incubator/mesos/trunk@1467841 13f79535-47bb-0310-9956-ffa450edef68
Replaced usleep() calls in libprocess with os::sleep().

From: Jiang Yan Xu <yan@jxu.me>
Review: https://reviews.apache.org/r/10241

git-svn-id: https://svn.apache.org/repos/asf/incubator/mesos/trunk@1467842 13f79535-47bb-0310-9956-ffa450edef68
Replaced sleep() and usleep() calls with os::sleep().

From: Jiang Yan Xu <yan@jxu.me>
Review: https://reviews.apache.org/r/10443

git-svn-id: https://svn.apache.org/repos/asf/incubator/mesos/trunk@1467843 13f79535-47bb-0310-9956-ffa450edef68