Update envetcd with output file option

Necessary to complete #82827528

PIVOTAL_TRACKER_STORY_URL=https://www.pivotaltracker.com/story/show/82979704
PIVOTAL_TRACKER_STORY_TYPE=feature
PIVOTAL_TRACKER_STORY_ESTIMATE=1
PIVOTAL_TRACKER_STORY_OWNER=jrubin
PIVOTAL_TRACKER_STORY_REQUESTER=jrubin
PIVOTAL_TRACKER_STORY_LABELS=envetcd, soaf