MI: mi_runto -pending

With the CLI testsuite's runto proc, we can pass "allow-pending" as an
option, like:

  runto func allow-pending

That is currently not possible with MI's mi_runto, however.  This
patch makes it possible, by adding a new "-pending" option to
mi_runto.

A pending breakpoint shows different MI attributes compared to a
breakpoint with a location, so the regexp returned by
mi_make_breakpoint isn't suitable.  Thus, add a new
mi_make_breakpoint_pending proc for pending breakpoints.

Tweak mi_runto to let it take and pass down arguments.

Change-Id: I185fef00ab545a1df2ce12b4dbc3da908783a37c