freebsd-update: do not restart jailed sshd

[emaste]

Summary

In 6cd1bc531609 for PR 263489 I changed freebsd-update to restart sshd after upgrade, to avoid an upgrade-related incompatibility that made it impossible to login.

This is intended to avoid losing access to remote hosts, and ought not apply to upgrading a jail.

PR: 263489, 272282

[emaste]

Test $BASEDIR instead of $JAIL; we should not do the sshd restart dance for -b either.

[otis]

I see inconsistent use of quotes around variable dereference (sometimes ${BASEDIR, sometimes "${BASEDIR}"). Other than that LGTM.

I'll test it on some jails I have left to update.

[otis]

Tested, working, LGTM.

[kevans]

I was going to complain from the description that I could only have access to the jail and be updating from within, but I reckon BASEDIR would be / in that case

[emaste]

I was going to complain from the description that I could only have access to the jail and be updating from within

Will update the commit message to make this clear