retrying LB node remove
added lb delete timeout in config
Merge branch 'lb_delete_refactor' into lb-delete-retry

Conflicts:
	otter/worker/launch_server_v1.py
lb node removal retry interval randomized

to avoid all DELETE at same time
lb add retry interval randomized
Non-422 failures are propogated

to allow 'Got LB error' logs.

This change is there in PR #565. So should have no effect when this
branched is merged with master having that PR merged
Retry config changes

random range and delete timeout
LB add/remove node tests updated
delete jobs are started in parallel
lint fixes
removed unnecessary change
Removed unused var - thanks @cyli
Remove stagerring related other changes - thanks @cyli
random_interval() function impl

that returns random interval each time it is called
Using new random_interval function - thanks @cyli

to randomly stagger lb add/delete retries
LB node removal does not timeout

- i.e. it does not use retry_and_timeout that can cancel a (possible)
    successful delete in progress. Instead uses retry_times like add_lb
    that finishes the request before deciding to try again
- Removed hard-code range [10, 15]
- modified remove_lb tests to include log checking also
- added remove_lb test for checking default configs being used
removed unwanted var
better function name - thanks @cyli
removed usage of unwanted var
use CheckFailure - thanks @cyli

instead of manual checking args by extracting it from mock.calls