Adds the support of two optionals parameters for the cron-trigger resource:
-first-execution-time : --first-time <"YYYY-MM-DD HH:MM">
-remaining_occurrences : --count <integer>
The positional parameter "pattern" is now: --pattern <"* * * * *">
Implements: blueprint mistral-cron-triggers-start-and-repeat
Depends-On: I55bc28e98f89ffdfdce9cb3daa3848a17d85fd20
Change-Id: I2059db83e217ff415fb3f43dca27904b8f9acdce