Revert "Revert "Add docker exec run a command in privileged mode""

This reverts commit 40b71adee3.

Original commit (for which this is effectively a rebased version) is
72a500e9e5 and was provided by Lei Jitang
<leijitang@huawei.com>.

Signed-off-by: Tim Dettrick <t.dettrick@uq.edu.au>

docs/reference/commandline/exec.md

@@ -17,6 +17,7 @@ weight=1
 
       -d, --detach=false         Detached mode: run command in the background
       -i, --interactive=false    Keep STDIN open even if not attached
+      --privileged=false         Give extended privileges to the command
       -t, --tty=false            Allocate a pseudo-TTY
       -u, --user=                Username or UID (format: <name|uid>[:<group|gid>])