Make print_command_trace varargs

Make print_command_trace varargs

I noticed some code in execute_control_command_1 that could be
simplified by making print_command_trace a printf-like function.  This
patch makes this change.

ChangeLog
2018-05-04  Tom Tromey  <tom@tromey.com>

	* top.c (execute_command): Update.
	* cli/cli-script.h (print_command_lines): Now varargs.
	* cli/cli-script.c (print_command_lines): Now varargs.
	(execute_control_command_1) <case while_control, case if_control>:
	Update.