ZTS: Eliminate random and shuf, consolidate code

Both GNU and FreeBSD sort have -R to randomize input.

Reviewed-by: John Kennedy <john.kennedy@delphix.com>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ryan Moeller <ryan@iXsystems.com>
Closes #9900

tests/zfs-tests/include/commands.cfg

@@ -123,7 +123,6 @@ export SYSTEM_FILES_FREEBSD='chflags
     mkfifo
     newfs
     pw
-    random
     rmextattr
     setextattr
     sha256
@@ -161,7 +160,6 @@ export SYSTEM_FILES_LINUX='attr
     setenforce
     setfattr
     sha256sum
-    shuf
     udevadm
     useradd
     userdel