Provide option to continue graphing objects that loose their index

[cigamit]

Is your feature request related to a problem? Please describe.
For data query objects that disappear after a timeout, like dialin users and the like, allow Cacti to continue to graph these interfaces instead of disabling their graphing. This may result in unknown data being inserted into the RRDfile, but when the transient data query object comes back online, it can resume graphing without a re-index

Describe the solution you'd like
Add a data query XML field to instruct cacti to ignore interfaces that disappear from a data query when re-indexing. Suggest introducing the data query XML field as follows:

<index_transient>true</index_transient>

When this field exists and is set to true, ignore the missing indexes and continue to graph them.

Describe alternatives you've considered
Cacti used to work this way by default, but this behavior changed in Cacti 1.2.x