mtail: cap memory to 800M

Swap is taken into account too in cgroups v1, disable it.
1 job for mtail_memory in 8 seconds (queued for 15 minutes and 25 seconds)
Status Job ID Name Coverage
  Test
failed #9050
ai3
run_base_test

00:00:08

 
Name Stage Failure
failed
run_base_test Test
VBoxManage: error: Could not create the imported medium '/home/gitlab-runner/VirtualBox VMs/stretch_1560611398220_85167/stretch.vmdk'.
VBoxManage: error: VMDK: cannot write allocated data block in '/home/gitlab-runner/VirtualBox VMs/stretch_1560611398220_85167/stretch.vmdk' (VERR_DISK_FULL)
VBoxManage: error: Details: code VBOX_E_FILE_ERROR (0x80bb0004), component ApplianceWrap, interface IAppliance
VBoxManage: error: Context: "RTEXITCODE handleImportAppliance(HandlerArg*)" at line 886 of file VBoxManageAppliance.cpp
ERROR: could not start virtual machines
~/builds/20519861/0/ai3/float/test/test-base ~/builds/20519861/0/ai3/float/test/test-base ~/builds/20519861/0/ai3/float/test
==> host1: VM not created. Moving on...
~/builds/20519861/0/ai3/float/test/test-base ~/builds/20519861/0/ai3/float/test
ERROR: Job failed: exit status 1