[Bug 1096276] signal 27 (SIGPROF) not passed to container using --sig-proxy

[Red Hat Bugzilla]

https://bugzilla.redhat.com/show_bug.cgi?id=1096276

--- Comment #12 from Matthew Heon  ---
Docs have been updated to indicate that SIGSTOP and SIGKILL are not proxied,
this should appear in the next RHEL build of Docker.

I'm hesitant to document the remaining few (SIGCONT and SIGPROF) given that
they are technically Golang bugs - if they're fixed, the documentation would no
longer be accurate.