rootfs-postcommands: Improve/fix rootfs_check_host_user_contaminated

Currently if the find command finds /home it stops checking the other
files. Tweak the find expression to fix this.

Also, from Alex Kiernan <alex.kiernan@gmail.com>, generate output for
each contaminated path so it's visible in the main log file.

When matches are found, dump the data from the group and passwd files
so useful debugging can be done based on the results.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>