Adjust coredump-filter.exp to account for NT_FILE note handling

This commit makes adjustments to coredump-filter.exp to account
for the fact that NT_FILE file-backed mappings are now available
when a core file is loaded.  Thus, a test which was expected
to PASS when a memory region was determined to be unavailable
(due to no file-backed mappings being available) will now FAIL
due to those mappings being available from having loaded the
NT_FILE note.

I had originally marked the test as XFAIL, but Mihails Strasuns
suggested a much better approach:

    1) First test that it still works if file is accessible in the
       filesystem.
    2) Temporarily move / rename the file and test that disassembly
       doesn't work anymore.

That's what this commit implements.

gdb/testsuite/ChangeLog:

	* gdb.base/coredump-filter.exp: Add second
	non-Private-Shared-Anon-File test.
	(test_disasm): Rename binfile for test which is expected
	to fail.