zdump: copy: add support for file output

It is unusual to write the file output from a tool to stdout. Therefore
add a positional argument to the zgetdump convert action where the
output file can be specified. If no positional argument is given the
output is written to stdout as before and therefore there is no change
in the default behavior.

If the file output already exists an error is returned. The reason for
this is to avoid the situation where an existing dump is accidentally
overwritten by the user.

Reviewed-by: Alexander Egorenkov <egorenar@linux.ibm.com>
Signed-off-by: Marc Hartmayer <mhartmay@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

zdump/Makefile

@@ -52,7 +52,7 @@ OBJECTS = zgetdump.o opts.o zg.o \
 	  df_elf.o df_s390.o \
 	  dt.o dt_s390sv.o dt_s390sv_ext.o \
 	  dt_s390mv.o dt_s390mv_ext.o \
-	  dt_scsi.o stdout.o \
+	  dt_scsi.o output.o
 
 ifeq ("$(HAVE_FUSE)","0")
 FUSE_CFLAGS = -DHAVE_FUSE=0 -D_FILE_OFFSET_BITS=64