Print bootstrap errors through ctx.Status

Blueprint bootstrap was printing the errors directly to stdout, which
resulted in a different format that the buildbots didn't recognize
and extract into build_error.log, and which soong_ui didn't put into
error.log.  Bootstrap then returned a single error "fatal errors
encountered", which was printed by soong_build and soong_ui.

Blueprint now returns all the errors and doesn't print anything,
and lets soong_build and soong_ui print all the errors isntead of
just "fatal errors encountered".  Change bootstrap in soong_ui to
feed the errors through ctx.Status, which will result in them being
handled like any other error, including writing to error.log and
adding the "FAILED:" header on stdout that the buildbots are looking
for.

Bug: 375389896
Test: build with a syntax error
Test: build with a soong error
Flag: EXEMPT host-only
Change-Id: Id4056cfc0e99a84ba05cb0abd9feb9f488a07822