* If a workflow is large then parsing a spec takes significant
time and it's too expensive to do it often. For example,
on a regular laptop parsing a workflow consisting from
100 tasks takes about 2 seconds. That was the reason why
such a workflow used to take so much time to start, ~200
seconds. This patch eliminates unnecessary parsing by
applying caching for workflow specifications.
Change-Id: Iabfdea2182a81cda07a8692f5b84c6bfb561bb83
5d51dfcc5b