Implement a configurable delay after an endview call.

This has been implemented after the following discussion thread
https://groups.google.com/d/msg/jenkinsci-users/cWNvmxBf1WI/Z_WHm_ay4VEJ

Apparently, when calling cleartool endview -server command, cleartool
may return before the view_server has been ended, which results in
errors for subsequent commands.

It is available as global configuration parameter.