Resolve little-ambiguous input as dasqueries. fixes issue #4081.

* support simple little amobigous patterns: dataset with three slashes, block, release, site
* currently no extra * are added (e.g. T1_US stays site=T1_US, not T1_US*)
  - this is possible, but shall not pass unnoticed, and shall only happen if no wildcard version gives no results
moved the regex rules into regex.py
Merge pull request #4089 from dmwm/unambigous_ql_patterns

Resolve little-ambiguous input as dasqueries. fixes issue #4081.