Fix gdb.base/term.exp on non-"target native" boards

With --target_board=native-extended-gdbserver, we get:

  Running .../src/gdb/testsuite/gdb.base/term.exp ...
  FAIL: gdb.base/term.exp: info terminal at breakpoint

  (gdb) info terminal
  No saved terminal information.

Fix it by running the test everywhere, and expecting different output
on non-native targets.

gdb/testsuite/ChangeLog:
2017-10-13  Pedro Alves  <palves@redhat.com>

	* gdb.base/term.exp: Don't skip if is_remote target.  Instead,
	expect different "info terminal" output if testing with a
	non-native target.