cache: improve out-of-disk condition

When suspect SIGBUS happens, print helpful error and try to remove
the cache, so that the service might work again if auto-restarted.
Theoretically we could longjmp() out of the SIGBUS handler,
but that would be rather messy, so let the process die.
23 jobs for <span class="ref-name">cache-sigbus</span> in 70 minutes and 1 second (queued for 7 seconds)
Status Job ID Name Coverage
  Build
passed #174684
docker linux amd64
build:clang:linux:amd64

00:00:42

passed #174683
docker linux amd64
build:linux:amd64

00:00:45

passed #174685
docker linux amd64 allowed to fail
srpm

00:00:24

 
  Test
passed #174692
docker linux amd64
deckard:linux:amd64

00:01:20

passed #174697
privileged
distro:epel-7

00:01:40

passed #174696
privileged
distro:fedora-29

00:02:16

passed #174691
docker
doc

00:00:44

passed #174690
docker linux amd64
installcheck:linux:amd64

00:01:02

passed #174693
docker linux amd64
installcheck:valgrind:linux:amd64

00:01:44

passed #174687
docker
lint:c

00:02:24

failed #174688
docker allowed to fail
lint:clang-scan-build

00:01:14

passed #174686
docker
lint:lua

00:00:33

passed #174695
docker linux amd64
respdiff:iter:udp:linux:amd64

00:02:26

passed #174689
docker linux amd64
test:linux:amd64

00:01:01

passed #174694
docker linux amd64
test:linux:amd64:valgrind

00:01:11

 
  Respdiff
passed #174698
respdiff
respdiff:fwd-tls6-kresd.udp6

00:24:28

passed #174699
respdiff
respdiff:fwd-udp6-kresd.udp6

00:42:58

passed #174703
respdiff
respdiff:fwd-udp6-unbound.tcp6

00:47:29

passed #174707
respdiff
respdiff:fwd-udp6-unbound.tls6

00:19:18

passed #174702
respdiff
respdiff:fwd-udp6-unbound.udp6

00:33:58

passed #174701
respdiff
respdiff:iter.tls6

00:34:59

passed #174700
respdiff
respdiff:iter.udp6

00:22:27

failed #174704
respdiff
respdiff:fwd-udp6-unbound.tls6

00:12:57

 
Name Stage Failure
failed
lint:clang-scan-build Test
  CCLD	modules/hints/hints.so
CCLD modules/stats/stats.so
CCLD modules/bogus_log/bogus_log.so
scan-build: 32 bugs found.
scan-build: Run 'scan-view /builds/knot/knot-resolver/scan-results/2018-09-14-065041-14-1' to examine bug reports.
Uploading artifacts...
scan-results: found 37 matching files
Uploading artifacts to coordinator... ok id=174688 responseStatus=201 Created token=CYYmxF7Q
ERROR: Job failed: exit code 1