format: blkid content check, format argument, and verbose argument

- Added new argument -force to the format utility. This will force formatting of the specified single device if it exists and is a block device
- By default, the format package will no longer format the specified single device if content exists on that device
- Added new blkid-based check for content, in addition to the existing check for partitions on autoformat candidate devices.
- Cleanup of old unused code.
- Refactoring of block device verification.
- Added test/cases/040_packages/006_format_mount/005_by_device_force
- Added document of new arguments to /docs/external-disk.md. Also sorted the arguments in the doc alphabetically and added them as bullets so they do not run together on the page.

Signed-off-by: Isaac Rodman <isaac@eyz.us>

test/cases/040_packages/006_format_mount/005_by_device_force/check.sh

@@ -0,0 +1,54 @@
+#!/bin/sh
+
+function failed {
+	printf "format_force test suite FAILED\n" >&1
+	exit 1
+}
+
+# sda should have been partitioned and sda1 formatted as ext4
+#   command: ["/usr/bin/format", "-verbose", "-type", "ext4", "/dev/sda"]
+
+# sdb should have been partitioned and sdb1 formatted as ext4
+#  command: ["/usr/bin/format", "-verbose", "-type", "ext4", "/dev/sdb"]
+
+# sda1 should remain ext4, as the format was not re-forced
+#  command: ["/usr/bin/format", "-verbose", "-type", "xfs", "/dev/sda"]
+
+# sdb should have been re-partitioned, with sdb1 now formatted as xfs due to -force flag
+#  command: ["/usr/bin/format", "-verbose", "-force", "-type", "xfs", "/dev/sdb"]
+
+ATTEMPT=0
+
+while true; do
+  ATTEMPT=$((ATTEMPT+1))
+
+  echo "=== forcing device discovery (attempt ${ATTEMPT}) ==="
+  mdev -s
+
+  echo "=== /dev list (attempt ${ATTEMPT}) ==="
+  ls -al /dev
+
+  if [ -b /dev/sda1 ] && [ -b /dev/sdb1 ]; then
+    echo 'Found /dev/sda1 and /dev/sdb1 block devices'
+    break
+  fi
+
+  if [ $ATTEMPT -ge 10 ]; then
+    echo "Did not detect /dev/sda1 nor /dev/sdb1 in ${ATTEMPT} attempts"
+    failed
+  fi
+
+  sleep 1
+done
+
+echo "=== /dev/sda1 ==="
+blkid -o export /dev/sda1
+echo "=== /dev/sdb1 ==="
+blkid -o export /dev/sdb1
+
+echo "=== /dev/sda1 test ==="
+blkid -o export /dev/sda1 | grep -Fq 'TYPE=ext4' || failed
+echo "=== /dev/sdb1 test ==="
+blkid -o export /dev/sdb1 | grep -Fq 'TYPE=xfs' || failed
+
+printf "format_force test suite PASSED\n" >&1

test/cases/040_packages/006_format_mount/005_by_device_force/test.sh

@@ -0,0 +1,26 @@
+#!/bin/sh
+# SUMMARY: Check that the format and mount packages work
+# LABELS:
+# REPEAT:
+
+set -e
+
+# Source libraries. Uncomment if needed/defined
+#. "${RT_LIB}"
+. "${RT_PROJECT_ROOT}/_lib/lib.sh"
+
+NAME=test-format
+DISK1=disk1.img
+DISK2=disk2.img
+
+clean_up() {
+	rm -rf ${NAME}-* ${DISK1} ${DISK2}
+}
+trap clean_up EXIT
+
+moby build -format kernel+initrd -name ${NAME} test.yml
+RESULT="$(linuxkit run -disk file=${DISK1},size=512M -disk file=${DISK2},size=512M ${NAME})"
+echo "${RESULT}"
+echo "${RESULT}" | grep -q "suite PASSED"
+
+exit 0

test/cases/040_packages/006_format_mount/005_by_device_force/test.yml

@@ -0,0 +1,37 @@
+kernel:
+  image: linuxkit/kernel:4.9.51
+  cmdline: "console=ttyS0"
+init:
+  - linuxkit/init:6fe9d31a53bbd200183bb31edd795305e868d5a7
+  - linuxkit/runc:a1b564248a0d0b118c11e61db9f84ecf41dd2d2a
+onboot:
+  - name: format
+    image: linuxkit/format:test
+    command: ["/usr/bin/format", "-verbose", "-type", "ext4", "/dev/sda"]
+  - name: format
+    image: linuxkit/format:test
+    command: ["/usr/bin/format", "-verbose", "-type", "ext4", "/dev/sdb"]
+  - name: format
+    image: linuxkit/format:test
+    command: ["/usr/bin/format", "-verbose", "-type", "xfs", "/dev/sda"]
+  - name: format
+    image: linuxkit/format:test
+    command: ["/usr/bin/format", "-verbose", "-force", "-type", "xfs", "/dev/sdb"]
+  - name: test
+    image: linuxkit/format:test
+    binds:
+      - /check.sh:/check.sh
+    command: ["sh", "./check.sh"]
+    capabilities:
+      - CAP_SYS_ADMIN
+      - CAP_MKNOD
+  - name: poweroff
+    image: linuxkit/poweroff:1e9876c682c74d0602b7647c628bb0875fb13998
+    command: ["/bin/sh", "/poweroff.sh", "10"]
+files:
+  - path: check.sh
+    source: ./check.sh
+trust:
+  org:
+    - linuxkit
+    - library