Momentary breakpoints should have no breakpoint number

Momentary breakpoints should have no breakpoint number

Momentary breakpoints have no breakpoint number, their breakpoint
number should be always 0, to avoid constantly incrementing (or
decrementing) the internal breakpoint count.

Indeed, set_momentary_breakpoint installs the created breakpoint
without a number.

However, momentary_breakpoint_from_master incorrectly gives an
internal breakpoint number to the new breakpoint.  This commit fixes
that.

Change-Id: Iedcae5432cdf232db9e9a6e1a646d358abd34f95