Lumberyard Beta 1.21.1 includes the following update:
Perforce no longer initializes by default in the Lumberyard Editor Perforce plugin. To initialize Perforce, set the address of the Perforce server in a P4PORT environment variable, using P4 SET P4PORT, or in a P4CONFIG file.
Read the GitHub release notes for 1.21.1 here.
Read the full Lumberyard Beta 1.21 Release Notes.