Upgrade gravitational teleport to 2.6.6.
- See upstream's changelog for details https://github.com/gravitational/teleport/blob/master/CHANGELOG.md
- Explicitly specify the git sha when building teleport.
- Restrict builds to amd64.
- Work around daemon(8)'s lack of syslog functionality in 10-STABLE.
Submitted by: swills
Approved by: swills (mentor)
Differential Revision: https://reviews.freebsd.org/D15311