Merge commit a4ae32c7 ("exec: Always set cap_ambient in cap_bprm_set_creds")

This is a bug fix and one of two places where I have found that the
result of calling security_bprm_repopulate_creds more than once on
different bprm->files depends on all of the bprm->files not just the
file bprm->file.

I intend to fix both of those cases and then modify the code to
only call security_bprm_repopulate_creds on the final bprm file.

So merge this change in so I hopefully reduce conflicts for others
and I make it possible to build on top of this change.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>