parameterize polling frequency for delay queue throttling algorithm

[d-w-moore]

Right now a collection operation spawns N jobs into the delay queue at a time. (N is basically a threshold set by the configuration variable "job_limit_per_collection_indexing_operation"). It does so by alternately sleeping a WAIT value hardwired to 1 second between queries of the count of currently active delay tasks. This WAIT value should ideally be configurable to reduce network traffic to the iRODS server.