gitlab-ci: run unit tests under valgrind in gitlab-ci

On Ubuntu 16.04 (trusty) valgrind fails due to rdrand being advertised
but not implemented.

Work around that by installing valgrind from Ubuntu 18.04 (bionic) via
the "contrib/scripts/nm-ci-install-valgrind-in-ubuntu1604.sh" script.
12 jobs for <span class="ref-name">th/gitlab-ci-valgrind</span> in 39 minutes and 42 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
passed #306503
allowed to fail
checkpatch

00:01:29

passed #306510
t_debian:9

00:16:57

passed #306512
t_debian:sid

00:17:03

passed #306514
allowed to fail manual
t_debian:testing

00:12:06

passed #306504
t_fedora:28

00:30:13

passed #306505
t_fedora:29

00:30:23

failed #306506
t_fedora:30

00:14:33

failed #306507
allowed to fail manual
t_fedora:rawhide

00:07:47

passed #306508
t_ubuntu:16.04

00:14:52

passed #306509
t_ubuntu:18.04

00:17:12

canceled #306511
allowed to fail manual
t_debian:testing

00:00:01

 
  External
canceled NetworkManager test verification

00:02:19

 
Name Stage Failure
failed
t_fedora:rawhide Test
./src/ndisc/tests/test-ndisc-fake.valgrind-log:   fun:(below main)
./src/ndisc/tests/test-ndisc-fake.valgrind-log:}
>>>> PRINT VALGRIND LOGS (valgrind test) (done)
valgrind test failed
+ echo '>>>> PRINT VALGRIND LOGS (valgrind test) (done)'
+ die 'valgrind test failed'
+ printf '%s\n' 'valgrind test failed'
+ exit 1
ERROR: Job failed: exit code 1
failed
t_fedora:30 Test
./libnm/tests/test-nm-client.valgrind-log:   fun:g_param_spec_string
./libnm/tests/test-nm-client.valgrind-log: fun:nm_device_class_init
./libnm/tests/test-nm-client.valgrind-log: fun:nm_device_class_intern_init
./libnm/tests/test-nm-client.valgrind-log: fun:type_class_init_Wm
./libnm/tests/test-nm-client.valgrind-log: fun:g_type_class_ref
./libnm/tests/test-nm-client.valgrind-log: fun:g_type_class_ref
./libnm/tests/test-nm-client.valgrind-log: fun:g_object_new_valist
./libnm/tests/test-nm-client.valgrind-log: fun:g_object_new
.
Job's log exceeded limit of 4194304 bytes.