Create directories before unzipping dexpreopt zip

unzip sometimes fails with:
checkdir error: cannot create out/target/product/.../system/framework/oat
File exists

I think this happens when two unzips run in parallel, see that the
parent directory is missing, race to create it, and then one of them
treats the EEXIST when creating it as an error instead of continuing.
Work around this by creating the directories with mkdir -p before
running unzip.

Test: m installclean && m
Bug: 119412419
Change-Id: Ie7daa94e107d53eff075ca58dbe721bd9d7fc8c2