Set the remote shell's OOM score adjustment value via its unit file, instead...

Set the remote shell's OOM score adjustment value via its unit file, instead of dynamically at test suite run time.

config/chroot_local-includes/lib/systemd/system/tails-autotest-remote-shell.service

@@ -7,6 +7,7 @@ Before=gdm.service
 [Service]
 Type=notify
 ExecStart=/usr/local/lib/tails-autotest-remote-shell /dev/ttyS0
+OOMScoreAdjust=-1000
 
 [Install]
 WantedBy=multi-user.target

features/step_definitions/erase_memory.rb

@@ -128,12 +128,6 @@ Given /^I fill the guest's memory with a known pattern(| without verifying)$/ do
     $vm.execute_successfully("sysctl #{key}=#{val}")
   end
 
-  # The remote shell is sometimes OOM killed when we fill the memory,
-  # and since we depend on it after the memory fill we try to prevent
-  # that from happening.
-  pid = $vm.pidof("tails-autotest-remote-shell")[0]
-  $vm.execute_successfully("echo '-1000' > /proc/#{pid}/oom_score_adj")
-
   # We exclude the memory we reserve for the kernel and admin
   # processes above from the free memory since fillram will be run by
   # an unprivileged user in user-space.