Allow running `arc patch` without authentication.
Allow running `arc patch` without authentication.

Summary:
Allow `arc patch` without authentication if Phabricator instance has
'differential.anonymous-access' set to true.

Test Plan:
Set 'differential.anonymous-access' in Phabricator to true and run `arc patch`
without installing a certificate.  `arc patch` should work as expected.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, epriestley

Differential Revision: 1069

chundongwang/arcanist,chundongwang/arcanist,hach-que/arcanist,wharris/arcanist,calblueprint/arcanist,haskell-infra/arcanist,sneakpeeq/arcanist,calblueprint/arcanist,eSpark/arcanist,wxstars/arcanist,Khan/arcanist,KieranHayes/arcanist,dguo-coursera/arcanist,sneakpeeq/arcanist,aik099/arcanist,sneakpeeq/arcanist,haskell-infra/arcanist,julkiewicz/arcanist,PageUpPeopleOrg/arcanist-patches,r4nt/arcanist,fivestars/arcanist,jra3/arcanist,sneakpeeq/arcanist,chundongwang/arcanist,julkiewicz/arcanist,folsom-labs/arcanist,uber/arcanist,memsql/arcanist,eSpark/arcanist,folsom-labs/arcanist,wikimedia/phabricator-arcanist,kevinseelbach/arcanist,Khan/arcanist,uber/arcanist,codelabs-ch/arcanist,coursera/arcanist,haskell-infra/arcanist,fivestars/arcanist,PageUpPeopleOrg/arcanist-patches,julkiewicz/arcanist,folsom-labs/arcanist,codelabs-ch/arcanist,wikimedia/phabricator-arcanist,wharris/arcanist,zhihu/arcanist,phacility/arcanist,hach-que/arcanist,Khan/arcanist,alexmv/arcanist,jra3/arcanist,hach-que/arcanist,jra3/arcanist,alexmv/arcanist,aik099/arcanist,memsql/arcanist,fivestars/arcanist,uber/arcanist,coursera/arcanist,aik099/arcanist,KieranHayes/arcanist,wxstars/arcanist,julkiewicz/arcanist,r4nt/arcanist,zhihu/arcanist,PageUpPeopleOrg/arcanist-patches,jra3/arcanist,dguo-coursera/arcanist,memsql/arcanist,coursera/arcanist,alexmv/arcanist,haskell-infra/arcanist,kevinseelbach/arcanist,uber/arcanist,eSpark/arcanist,hach-que/arcanist,wxstars/arcanist,r4nt/arcanist,Khan/arcanist,zhihu/arcanist,coursera/arcanist,KieranHayes/arcanist,dguo-coursera/arcanist,wharris/arcanist,chundongwang/arcanist,folsom-labs/arcanist,wxstars/arcanist,aik099/arcanist,phacility/arcanist,zhihu/arcanist,eSpark/arcanist,KieranHayes/arcanist,codelabs-ch/arcanist,calblueprint/arcanist,Symplicity/arcanist,kevinseelbach/arcanist,phacility/arcanist,codelabs-ch/arcanist,Symplicity/arcanist,kevinseelbach/arcanist,r4nt/arcanist,codelabs-ch/arcanist,fivestars/arcanist,Symplicity/arcanist,dguo-coursera/arcanist,Symplicity/arcanist,PageUpPeopleOrg/arcanist-patches,alexmv/arcanist,wharris/arcanist,phacility/arcanist,wikimedia/phabricator-arcanist,calblueprint/arcanist,wikimedia/phabricator-arcanist,phacility/arcanist,memsql/arcanist