Make DAP instruction breakpoints unverified

Currently, when a DAP client uses setInstructionBreakpoints, the
resulting breakpoints are created as "verified", even though there is
no symbol file and thus the breakpoint can't possibly have a source
location.

This patch changes the DAP code to assume that all breakpoints are
unverified before launch.

Reviewed-by: Keith Seitz <keiths@redhat.com>