Overwrite ${board}_file in local-remote-host

After I run test like this,

 $ make check RUNTESTFLAGS='--host_board=local-remote-host dw2-basic.exp'

gdb.dwarf2/file1.txt in source tree was removed.  In some gdb.dwarf2/*.exp,
file1.txt is copied to host and then removed at the end.  However, in
local-remote-host-notty.exp, ${board}_download doesn't copy the file but
return the absolute path of the src file.  'remote_file host delete' at
the end will remove the file in source tree.

This patch is to overwrite ${board}_file, and specially make "delete"
option do nothing.  This approach is used in gdbserver-base.exp and
remote-stdio-gdbserver.exp too.

gdb/testsuite:

2014-05-14  Yao Qi  <yao@codesourcery.com>

	* boards/local-remote-host-notty.exp (${board}_file): New
	proc.

gdb/testsuite/ChangeLog

@@ -1,3 +1,8 @@
+2014-05-14  Yao Qi  <yao@codesourcery.com>
+
+	* boards/local-remote-host-notty.exp (${board}_file): New
+	proc.
+
 2014-05-07  Kyle McMartin  <kyle@redhat.com>
 
 	Pushed by Joel Brobecker  <brobecker@adacore.com>.

gdb/testsuite/boards/local-remote-host-notty.exp

@@ -33,6 +33,13 @@ set_board_info rsh_prog /usr/bin/ssh
 set_board_info rcp_prog /usr/bin/scp
 set_board_info file_transfer "rsh"
 
+proc ${board}_file { dest op args } {
+    if { $op == "delete" } {
+	return 0
+    }
+    return [eval [list standard_file $dest $op] $args]
+}
+
 proc ${board}_download { board src dest } {
 
     # If file name is a relative, convert it to absolute, otherwise file can't