zfcpdump: Add install script for zfcpdump

Since version 198 (Feb 2013) systemd contains kernel-install, a script
managing kernel installs. This script allows execution of drop-in scripts
for customization. Add such a drop-in script to s390-tools to handle the
installation of zfcpdump kernels.

It's main purpose is to manage a link to the latest installed zfcpudump
kernel at ZFCPDUMP_IMAGE, where zipl expects to find the image to install
for a SCSI dumper.

The script supports two installation modes. One recommended by the
BootLoaderSpecs [1] to /boot/<machine-id>/<kernel-version> directories and
one directly to /boot. In the second case files are renamed during
installation to <original-name>-<kernel-version> to guarantee unique names.

Because the zfcpdump kernel is so special make the script stand-alone and
prevent any other script from being executed (exit 77) when a zfcpdump is
installed. Especially avoid functionality like creating an initrd (already
provided by s390-tools) or creating a boot entry (the zfcpdump kernel
should not be used for any other purpose than dumping).

The script requires systemd >= 203.

[1] https://www.freedesktop.org/wiki/Specifications/BootLoaderSpec/

Signed-off-by: Philipp Rudo <prudo@linux.ibm.com>
Reviewed-by: Hendrik Brueckner <brueckner@linux.ibm.com>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

.gitignore

@@ -77,6 +77,7 @@ zdump/zgetdump
 zfcpdump/cpioinit
 zfcpdump/zfcpdump_part
 zfcpdump/zfcpdump-initrd
+zfcpdump/10-zfcpdump.install
 ziomon/ziomon_mgr
 ziomon/ziomon_util
 ziomon/ziomon_zfcpdd