atomic: Use the masher user instead of rpmostreecompose

We need this because we'll be composing trees as the bodhi user

roles/atomic-composer/tasks/main.yml

@@ -3,15 +3,11 @@
 
 - yum: name=fedmsg-atomic-composer state=present enablerepo=infrastructure-testing
 
-- user: name=rpmostreecompose
+- user: name=masher
         shell=/bin/bash
         groups="mock,fedmsg"
-        generate_ssh_key=yes
   register: user
 
-- authorized_key: user={{ user['name'] }}
-                  key="{{ user['ssh_public_key'] }}"
-
 - file: path=/srv/fedora-atomic/
         owner={{ user['name'] }} group={{ user['name'] }} mode=755 state=directory