references to mdadm from otherwise generic code.
(grub_util_exec_pipe): Likewise.
(grub_util_exec_pipe_stderr): Likewise.
* grub-core/osdep/unix/getroot.c (grub_util_pull_lvm_by_command):
This function calls vgs, not mdadm; adjust variable names
accordingly.
the function of these files exceeds what can be sanely handled in shell
in posix-comaptible way. Also writing it in C extends the functionality
to non-UNIX-like OS and minimal environments.
