Make possible to specify a period of time for which nexus should not run any tasks

This param will force the TasksWaitForPlexusResource helper resource to not return immediately if tasks are not running, but wait for a period of time (windows) in which no tasks are being run

Signed-off-by: Alin Dreghiciu <adreghiciu@gmail.com>
Merge pull request #101 from sonatype/window-param-wait-for-tasks

REVIEW: Make possible to specify a period of time for which nexus should not run any tasks