Allow user and password in Zookeeper URL

This allow us to use a Zookeeper URL like: zk://user1:pass1@host1:123,host2,host3:312/path
Fix docs for constraints
fixes #668 - debug logging when tasks wasn't launched due to backoff
fixes #709 - flaky test DeploymentActorTest.Restart
use foreach instead of map
Merge pull request #711 from mesosphere/wip-709-fix-flaky-test-drexin

fixes #709 - flaky test DeploymentActorTest.Restart
Formatting: allow a long line in StartingBehavior.
Merge pull request #713 from mesosphere/line-length-exception

Formatting: allow a long line in StartingBehavior.
fixed debug log message in MarathonScheduler
log backoff message at INFO level
Merge pull request #710 from stem/master

Support Mesos Framework Authentication
Merge pull request #693 from iven/docs

Fix docs for constraints
Merge pull request #581 from iven/master

Allow user and password in Zookeeper URL
log backoff time left
Merge pull request #708 from mesosphere/wip-668-debug-logging-drexin

fixes #668 - debug logging when tasks wasn't launched due to backoff