Suppress stderr from expected-failure commands

Cleanup commands in prepare-testmachine-chroot (fuser, umount) may fail
when there is nothing to kill or unmount, producing confusing error
output in Jenkins logs. Redirect their output to /dev/null, matching the
pattern already used in test-on-testmachine lines 94 and 96.

Also suppress stdout/stderr from ps|grep process checks in
test-on-testmachine that look for known benign processes (minilogd,
gpg-agent). We only care about the exit code, not the output, so use
grep -q and redirect ps stderr.

Ticket: ENT-12619
Signed-off-by: Lars Erik Wik <lars.erik.wik@northern.tech>
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: larsewi

build-scripts/prepare-testmachine-chroot

@@ -21,9 +21,9 @@ CHROOT_ROOT=$HOME/testmachine-chroot/
 sudo mkdir -p "$CHROOT_ROOT"
 
 # Clean up previous chroot state by killing any processes that are using the CHROOT_ROOT directory.
-sudo "$FUSER" -k "$CHROOT_ROOT" || true
+sudo "$FUSER" -k "$CHROOT_ROOT" >/dev/null 2>&1 || true
 # Unmount the /proc filesystem if it was previously mounted inside the chroot.
-sudo umount "${CHROOT_ROOT}proc" || true
+sudo umount "${CHROOT_ROOT}proc" >/dev/null 2>&1 || true
 
 # Tell rsync not to touch the BASEDIR and PREFIX directories
 echo "P $BASEDIR" >"$TRANSFER_SCRIPT"

build-scripts/test-on-testmachine

@@ -51,23 +51,23 @@ chroot)
             # Minilogd may sometimes launch on RedHat without any user
             # intervention. Ignore that.
             # shellcheck disable=SC2009
-            if ps -ef | grep -E "^ *[^ ]+ +$pid" | grep minilogd; then
+            if ps -ef 2>/dev/null | grep -E "^ *[^ ]+ +$pid" | grep -q minilogd; then
                 continue
             fi
             ;;
         suse)
 
             # gpg-agent sometimes is spawned on suse during our tests.
             # This happens only in chroot. Ignore that.
-            if ps -o command --pid "$pid" | grep "gpg-agent --homedir /var/tmp/zypp.*zypp-trusted.*--daemon"; then
+            if ps -o command --pid "$pid" 2>/dev/null | grep -q "gpg-agent --homedir /var/tmp/zypp.*zypp-trusted.*--daemon"; then
                 continue
             fi
             ;;
         ubuntu)
             # gpg-agent sometimes is spawned on Ubuntu 24 during our tests.
             # This happens only in chroot. Ignore that.
             if [ "$OS_VERSION_MAJOR" = "24" ]; then
-                if ps -o command --pid "$pid" | grep "gpg-agent --homedir /etc/apt/sources.list.d/.gnupg-temp --use-standard-socket --daemon"; then
+                if ps -o command --pid "$pid" 2>/dev/null | grep -q "gpg-agent --homedir /etc/apt/sources.list.d/.gnupg-temp --use-standard-socket --daemon"; then
                     continue
                 fi
             fi