v4.6 keepalive not active when rampup or duration is 0

[sm-shaw]

In v4.6 replacement for runtimer the keepalive time is automatically calculated, however if rampup or duration is 0 it reports the error that the values cannot be detected. The margin for the keepalive time is also fixed but should be user configurable.
Also in v4.6 automation of loadscript for vucreate only loads the script the first time without doing the creation, it should do both.