Fix missing validation dataset, whitelist certain keywords for datasets
Signed-off-by: smajumdar <smajumdar@nvidia.com>

# What does this PR do ?

Fix adapters training script when there are no validation configs.

**Collection**: [ASR]

# Changelog 
- Fix validation config bug 
- Improve the handling of dataloader speeds in ASR

**PR Type**:
- [ ] New Feature
- [x] Bugfix
- [ ] Documentation
