Rename "set-endpoint" to "add-endpoint" in order to unify it and other commands

[yosukehara]

The prefix of current commands are "add", "create", "delete" and "update":

[S3-related Maintenance]
create-user ${user-id} [${password}]
delete-user ${user-id}
update-user-role ${user-id} ${role-id}
update-user-password ${user-id} ${password}
get-users
set-endpoint ${endpoint}
delete-endpoint ${endpoint}
get-endpoints
add-bucket ${bucket} ${access-key-id}
delete-bucket ${bucket} ${access-key-id}
get-buckets
update-acl ${bucket} ${access-key-id} private|public-read|public-read-write
get-acl ${bucket} ${access-key-id}

[yosukehara]

DONE - leo-project/leo_manager@aaeea75

add-endpoint leofs.test
OK

get-endpoints
endpoint         | created at
-----------------+---------------------------
s3.amazonaws.com | 2013-11-13 18:10:43 +0900
leofs.test       | 2013-11-13 18:10:56 +0900
localhost        | 2013-11-13 18:10:43 +0900