Allow passing library name with flag

Summary: Enables the process to pass the user input for library name. Fixes T3342

Test Plan: Little help... `arc liberate` doesn't run on windows. Though I saw the flag :)

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T3342

Differential Revision: https://secure.phabricator.com/D6306