* 'in_context' field of task executions changed its semantics to
not store workflow input and other data stored in the initial
workflow context such as openstack security context and workflow
variables, therefore task executions occupy less space in DB
* Introduced ContextView class to avoid having to merge
dictionaries every time we need to evaluate YAQL functions
against some context. This class is a composite structure
built on top of regular dictionaries that provides priority
based lookup algorithm over these dictionaries. For example,
if we need to evaluate an expression against a task inbound
context we just need to build a context view including
task 'in_context', workflow initial context (wf_ex.context)
and workflow input dictionary (wf_ex.input). Using this
class is a significant performance boost
* Fixed unit tests
* Other minor changes
Change-Id: I7fe90533e260e7d78818b69a087fb5175b9d5199
(cherry picked from commit a4287a5e63)
2ab055b57f