repart: Add --oem and OEM=

--oem can be used to only install OEM partitions (usr, verity,
verity-sig, ...). OEM= is used to indicate OEM partitions. If unset,
defaults to !FactoryReset. We also add a credential repart.oem to
allow configuring --oem via a credential.

test/units/testsuite-58.sh

@@ -132,6 +132,9 @@ EOF
 Type=home
 Label=home-first
 Label=home-always-too-long-xxxxxxxxxxxxxx-%v
+# Test that OEM=yes makes sure that a partition is OEM even if FactoryReset=yes is set.
+FactoryReset=yes
+OEM=yes
 EOF
 
     tee "$defs/swap.conf" <<EOF
@@ -139,6 +142,8 @@ EOF
 Type=swap
 SizeMaxBytes=64M
 PaddingMinBytes=92M
+# No OEM=yes here so this should not be considered an OEM partition since FactoryReset=yes.
+FactoryReset=yes
 EOF
 
     systemd-repart --offline="$OFFLINE" \
@@ -160,6 +165,26 @@ last-lba: 2097118
 $imgs/zzz1 : start=        2048, size=     1775576, type=933AC7E1-2EB4-4F13-B844-0E14E2AEF915, uuid=4980595D-D74A-483A-AA9E-9903879A0EE5, name=\"home-first\", attrs=\"GUID:59\"
 $imgs/zzz2 : start=     1777624, size=      131072, type=0657FD6D-A4AB-43C4-84E5-0933C84B4F4F, uuid=78C92DB8-3D2B-4823-B0DC-792B78F66F1E, name=\"swap\""
 
+    systemd-repart --offline="$OFFLINE" \
+                   --definitions="$defs" \
+                   --dry-run=no \
+                   --seed="$seed" \
+                   --empty=force \
+                   --include-partitions=home,swap \
+                   --oem=yes \
+                   --offline="$OFFLINE" \
+                   "$imgs/zzz"
+
+    output=$(sfdisk -d "$imgs/zzz" | grep -v -e 'sector-size' -e '^$')
+
+    assert_eq "$output" "label: gpt
+label-id: 1D2CE291-7CCE-4F7D-BC83-FDB49AD74EBD
+device: $imgs/zzz
+unit: sectors
+first-lba: 2048
+last-lba: 2097118
+$imgs/zzz1 : start=        2048, size=     2095064, type=933AC7E1-2EB4-4F13-B844-0E14E2AEF915, uuid=4980595D-D74A-483A-AA9E-9903879A0EE5, name=\"home-first\", attrs=\"GUID:59\""
+
     systemd-repart --offline="$OFFLINE" \
                    --definitions="$defs" \
                    --dry-run=no \