Fix lxc-ps -- argument processing

Fix lxc-ps -- argument processing

lxc-ps is supposed to pass arguments after the -- on to ps. The problem is
that i is expanded once from $@ and the loop will iterate over all the
arguments that were in $@ at the time of expansion. Inside the loop, there
are shifts (in the name case for example) that are trying to remove more
than a single argument. This changes fixes that and makes lxc-ps work as
documented.

Signed-off-by: Dwight Engen <dwight.engen@oracle.com>
Signed-off-by: Daniel Lezcano <dlezcano@fr.ibm.com>