coredump: report missing files without a backtrace

New message:

 ERROR: Required file /usr/lib64/libcrypto.so.3.0.1 not found.
 Exiting

Old message:

   File "/home/criu/coredump/criu_coredump/coredump.py", line 693, in _gen_mem_chunk
     f = open(fname, 'rb')
 FileNotFoundError: [Errno 2] No such file or directory: '/usr/lib64/libcrypto.so.3.0.1'

Signed-off-by: Adrian Reber <areber@redhat.com>

coredump/coredump.py

@@ -1,5 +1,6 @@
 import argparse
 import os
+import sys
 
 import criu_coredump
 
@@ -34,7 +35,12 @@ def main():
 
     opts = vars(parser.parse_args())
 
-    coredump(opts)
+    try:
+        coredump(opts)
+    except SystemExit as error:
+        print('ERROR: %s' % error)
+        print('Exiting')
+        sys.exit(1)
 
 
 if __name__ == '__main__':

coredump/criu_coredump/coredump.py

@@ -692,7 +692,11 @@ class coredump_generator:
             files = self.reg_files
             fname = next(filter(lambda x: x["id"] == shmid, files))["name"]
 
-            f = open(fname, 'rb')
+            try:
+                f = open(fname, 'rb')
+            except FileNotFoundError:
+                sys.exit('Required file %s not found.' % fname)
+
             f.seek(off)
 
         start = vma["start"]