Check with stdengine only

[muzimuzhi]

Useful when a quick check is wanted, especially when the test suite is quite large, e.g., in LaTeX2e base and l3kernel.

• Already discussed in small improvements for -S switch #320 (see "The second is ...")
• Loosely related to Output on failure does not help #341

Since the stdengine may differ across config files, any l3build check -e <specific-engine> may fail for some of the configs, as shown in linked issues.

Perhaps rather than -e<engine> we could do with a switch to use only the standard/default check engine (so --default/-d, or --standard-engine or ...)?
_{Originally posted by @josephwright in #320 (comment)}

[josephwright]

Yeah, I was thinking along these lines for #341 in particular - either the test should be skipped entirely or (more useful) we should just use the default engine

[josephwright]

I will put in a PR shortly. I was thinking again about the naming: as we always use stdengine, how about -s|--stdengine? (-s is currently unused).