This solves issues for rsync jobs for mirrors.

seems like copy removes destination if source does not exist so
we ended up with a buildrepo that removed all packages

This will hopefully fix the checksum errors

and generate index if it is missing, even if all packages are up2date.

and dont build index if its not needed

This will let user specify a directory where the repositories are.
Setting REPODEST will override PKGDEST.

the dependency repo tells apk index that dependencies are found
in another repository.