Fixing inline expressions evaluation
Fixing inline expressions evaluation

* In case if internal evaluated value is not a string (e.g. a number) it
  threw coercion exception

Change-Id: I0bf7dd3177a831bc119f75601011fcd8327272be

openstack/mistral,dennybaa/mistral,StackStorm/mistral,dennybaa/mistral,TimurNurlygayanov/mistral,StackStorm/mistral,openstack/mistral