Use logcache client default walk delay when getting latest envelope
Use logcache client default walk delay when getting latest envelope

- We may want to drop this to zero explicitly, but using a smaller value
than we're using in our ultimate Walk seems to address the problem where
we continually fail to see recent logs for both Docker and standard
workload pushes

[#172322729](https://www.pivotaltracker.com/story/show/172322729)

cloudfoundry/cli,cloudfoundry/cli,cloudfoundry/cli