Allow multiple *Validator classes to generate occurrences for the same rule

[barbeau]

Summary:

In https://github.com/CUTR-at-USF/gtfs-realtime-validator/issues/225 we found that currently all occurrences for the same rule need to be generated from the same *Validator class.

For optimization purposes, some of W009 checks for stop_time_updates were implemented in StopTimeUpdateValidator, while the checks specific to trips were implemented in TripDescriptorValidator. However, this currently causes problems when the *Validator classes are executed in BackgroundTask, as each class inserts a set of occurrences for the rules into the database, which caused a duplicate entry for occurrences of W009 (instead of all W009 occurrences properly being inserted in a single entry). Moving all checks for the same rule into the same class was the workaround solution implemented for W009 in https://github.com/CUTR-at-USF/gtfs-realtime-validator/commit/3bca917f3a2840d640c83a1d0e07c43cb8766cb0.

In the future we should examine allowing more than one *Validator class to check for the same rule, which would require modifications to BackgroundTask to combine occurrence lists from multiple *Validator classes before they are inserted into the database.

Steps to reproduce:

1. Have more than one Validator class generate occurrences for the same rule (for example W009 - revert this commit https://github.com/CUTR-at-USF/gtfs-realtime-validator/commit/3bca917f3a2840d640c83a1d0e07c43cb8766cb0).

Expected behavior:

The tool should log all occurrences correctly no matter what *Validator class generates them

Observed behavior:

If more than one *Validator class generates occurrences for the same rule, it results in more than one database record for that rule for a given iteration, which results in duplicate iterations being shown in the Log and IterationDetails page, and an invalid timestamp value of 1970... - see https://github.com/CUTR-at-USF/gtfs-realtime-validator/issues/225 for details.

Platform:

Windows 7 Enterprise w/ jdk1.8.0_73 and Chrome Version 58.0.3029.110 (64-bit)