* gdb.mi/mi-nonstop.exp: Don't check isnative. Use

	* gdb.mi/mi-nonstop.exp: Don't check isnative.  Use
	mi_run_to_main.  Skip thread exit test on remote targets.
	* gdb.mi/mi-nsintrall.exp: Don't check isnative.  Use
	mi_run_to_main.
	* gdb.mi/mi-nsmoribund.exp: Don't check isnative.  Use
	mi_run_to_main.
	* lib/mi-support.exp (mi_gdb_target_cmd): Remove trailing anchor
	when expecting ^connected.  Detect when the target doesn't support
	non-stop mode.
	(mi_run_cmd): Detect if non-stop mode was requested by isn't
	supported.  Return -1 on error, 0 on success.
	(mi_runto_helper): Don't expect a stop if mi_run_cmd failed.
	(mi_runto): Return mi_runto_helper's result explicitly.