Pass DOT_M2_SETTINGS to all invocations of sbt in marathon.groovy
Pass DOT_M2_SETTINGS to all invocations of sbt in marathon.groovy

Summary: Wrapped all executions of sbt with withCredentials, because AFAIK, any of them can trigger artifact downloading.

Test Plan: Execute a few Jenkins jobs

Reviewers: jasongilanfarr, timcharper, jeschkies, jenkins

Reviewed By: jasongilanfarr, jeschkies, jenkins

Subscribers: marathon-dev, aquamatthias, timcharper, jasongilanfarr, jeschkies

JIRA Issues: MARATHON-7214

Differential Revision: https://phabricator.mesosphere.com/D715

janisz/marathon,mesosphere/marathon,mesosphere/marathon,Caerostris/marathon,janisz/marathon,meln1k/marathon,natemurthy/marathon,meln1k/marathon,guenter/marathon,mesosphere/marathon,gsantovena/marathon,guenter/marathon,meln1k/marathon,natemurthy/marathon,janisz/marathon,Caerostris/marathon,gsantovena/marathon,guenter/marathon,guenter/marathon,janisz/marathon,mesosphere/marathon,natemurthy/marathon,gsantovena/marathon,gsantovena/marathon,Caerostris/marathon,gsantovena/marathon,meln1k/marathon,janisz/marathon,meln1k/marathon,Caerostris/marathon,guenter/marathon,mesosphere/marathon,Caerostris/marathon