modify commands to support a host system using bsdutils

The most popular coreutils implementations on Linux are GNU coreutils and busybox. There is another developed by Chimera Linux for their FreeBSD userland called chimerautils. chimerautils is based on bsdutils, so it should share functionality.

This MR modifies various command calls within pmbootstrap to better accommodate for bsdutils/chimerautils. Without this MR various pmbootstrap commands fail due to invalid command flags or syntax.