Support for querying the arcrest info endpoint in archery-manage

archery-manage now uses the arcrest info endpoint for endpoint discovery on ARC CE.

This is also now a default method with fall-back to LDAP GLUE2 when topology is specified as a list of ARC CEs.

I don't have any strong opinion regarding cherry-picking it to master. As production REST is ARC7, this part can be ARC7-only as well.