[CommCoreModule] Add endpoint: string arg to CommCoreModule.openSocket()

Summary:
Right now we're just hardcoding in localhost

[ignore: D3125]

Test Plan: Haven't tested with anything other than localhost... but continues to build/work as expected

Reviewers: ashoat, varun, def-au1t, karol-bisztyga, jimpo

Reviewed By: ashoat

Subscribers: palys-swm, Adrian, benschac

Differential Revision: https://phabricator.ashoat.com/D3127