Allow strip.sh --keep-mini-debug-info to work on non-elf files

strip.sh --keep-mini-debug-info matches the default for Make, and
is currently used on lots of files that are not elf files.  For
now, just make the behavior match Make and skip files when
strip --strip-all fails.

Bug: 113936524
Test: m checkbuild
Change-Id: I3648c914c0fd7cc9b68aa93fd3cb0b77504d42f6