Currently, the `exec` driver is only setting the Bounding set, which is
not sufficient to actually enable the requisite capabilities for the
task process.  In order for the capabilities to survive `execve`
performed by libcontainer, the `Permitted`, `Inheritable`, and `Ambient`
sets must also be set.

Per CAPABILITIES (7):

> Ambient: This is a set of capabilities that are preserved across an
> execve(2) of a program that is not privileged.  The ambient capability
> set obeys the invariant that no capability can ever be ambient if it
> is not both permitted and inheritable.

Fixes: hashicorp#16642