daemon/tls session tickets: avoid bad scheduling cycles

This should fix #385: possible floods with
> scheduling rotation check in 0 ms
18 jobs for tls-tickets-0ms in 8 minutes and 25 seconds (queued for 7 seconds)
Status Job ID Name Coverage
  Build
passed #153603
amd64 linux docker
build:clang:linux:amd64

00:00:49

passed #153602
amd64 linux docker
build:linux:amd64

00:00:49

passed #153604
amd64 linux docker allowed to fail
srpm

00:00:26

 
  Test
passed #153611
amd64 linux docker
deckard:linux:amd64

00:07:12

passed #153618
privileged
distro:epel-7

00:02:40

passed #153617
privileged
distro:fedora-27

00:03:41

passed #153610
docker
doc

00:00:43

passed #153609
amd64 linux docker
installcheck:linux:amd64

00:01:42

passed #153612
amd64 linux docker
installcheck:valgrind:linux:amd64

00:02:08

passed #153606
docker
lint:c

00:02:50

failed #153607
docker allowed to fail
lint:clang-scan-build

00:01:09

passed #153605
docker
lint:lua

00:00:43

passed #153615
amd64 linux docker
respdiff:iter:tcp:linux:amd64

00:04:05

passed #153616
amd64 linux docker
respdiff:iter:tls:linux:amd64

00:04:02

passed #153614
amd64 linux docker
respdiff:iter:udp:linux:amd64

00:04:06

passed #153608
amd64 linux docker
test:linux:amd64

00:01:16

passed #153613
amd64 linux docker
test:linux:amd64:valgrind

00:01:26

 
  Coverage
passed #153619
amd64 linux docker
coverage

00:00:23

70.2%
 
Name Stage Failure
failed
lint:clang-scan-build Test
                                             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
5 warnings generated.
CCLD daemon/kresd
scan-build: 29 bugs found.
scan-build: Run 'scan-view /builds/knot/knot-resolver/scan-results/2018-07-24-161042-14-1' to examine bug reports.
Uploading artifacts...
scan-results: found 34 matching files
Uploading artifacts to coordinator... ok
id=153607 responseStatus=201 Created token=xaL7FAyU
ERROR: Job failed: exit code 1