tools/hotplug: every systemd service depends on proc-xen.mount

tools/hotplug: every systemd service depends on proc-xen.mount

Every systemd service file uses /proc/xen/capabilites to check if it
runs in a dom0. Update every service file to enable proc-xen.mount with
the Requires= statement and schedule its startup with the After=
statement.
In some places var-lib-xenstored.mount is removed. This is ok because
its optional and this unit is enabled by xenstored itself. After all its
a private directory for xenstored.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: Ian Jackson <ian.jackson@eu.citrix.com>
Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Cc: Wei Liu <wei.liu2@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>