Having issue to support app property for loop delay field

[lixingwang]

Current behavior (how does the issue manifest):
Error report after configuring app property with loop delay field

error creating task [StartaSubFlow] in flow [dd]: strconv.Atoi: parsing "=$property[\"SyncStatus.Delay.DelayTime\"]": invalid syntax

Expected behavior:
Able to use app property in the delay field without any issue
Minimal steps to reproduce the problem (not required if feature enhancement):

Please tell us about your environment (Operating system, docker version, browser & web ui version, etc):

Flogo version (CLI & contrib/lib. If unknown, leave empty or state unknown): 0.X.X

Additional information you deem important (e.g. issue happens only occasionally):