build: the unix paths retire — configuration, logs, and volumes move into the danos tree

/etc/init.csv and /etc/devices.csv become /system/configuration/*.csv (the
repo's etc/ moves to system/configuration/, mirroring the runtime tree),
/var/log becomes /system/logs, and /mnt/usb becomes /volumes/usb. The
kernel VFS gains a carve-out so FAT may serve exactly /system/configuration
and /system/logs beneath the initrd-backed /system while /system and /test
themselves stay unshadowable; FAT's single /var mount splits into those two
rewritten mounts. The kvfs readdir check learns /system's third child and
the ramdisk spawn sweep skips the configuration tree.

Suite 106/106.

test/qemu_test.py

@@ -172,7 +172,7 @@ CASES = [
      "smp":    4,
      "timeout": 150,
      "qemu_extra": ["-device", "intel-iommu,intremap=off"],
-     "expect": r"(?s)(?=.*/system/kernel: iommu online)(?=.*fat: mounted /mnt/usb)(?=.*fat-test: ok)",
+     "expect": r"(?s)(?=.*/system/kernel: iommu online)(?=.*fat: mounted /volumes/usb)(?=.*fat-test: ok)",
      "fail":   r"DANOS-TEST-RESULT: FAIL|DANOS-IOMMU-FAULT"},
     # DMA + MSI under translation: interrupt-IN reports arrive through translated DMA and
     # the xHC's MSI/MSI-X still delivers (the 0xFEE00000 interrupt window bypasses second-
@@ -208,7 +208,7 @@ CASES = [
      "smp":    4,
      "timeout": 150,
      "qemu_extra": ["-device", "amd-iommu,dma-remap=on,intremap=off"],
-     "expect": r"(?s)(?=.*iommu online \(AMD-Vi\))(?=.*fat: mounted /mnt/usb)(?=.*fat-test: ok)",
+     "expect": r"(?s)(?=.*iommu online \(AMD-Vi\))(?=.*fat: mounted /volumes/usb)(?=.*fat-test: ok)",
      "fail":   r"DANOS-TEST-RESULT: FAIL|DANOS-IOMMU-FAULT"},
     # Port I/O grants: a claimed device's io_port resource lets a driver read/write its
     # ports (PS/2 status 0x64), gated by the claim; out-of-range/unclaimed is refused.
@@ -623,13 +623,13 @@ CASES = [
      "expect": r"usb-storage: ready[\s\S]*usb-storage: block 0 signature 0x55aa",
      "fail":   r"DANOS-TEST-RESULT: FAIL"},
     # FAT mount end to end: the fat server mounts the boot usb-storage device (the
-    # FAT32 image) into the VFS at /mnt/usb. A fat-test client then lists and reads
+    # FAT32 image) into the VFS at /volumes/usb. A fat-test client then lists and reads
     # through the mount — proof of the whole stack: block device -> FAT parse ->
     # VFS routing -> file read.
     {"name": "fat-mount",
      "smp":    4,
      "timeout": 150,
-     "expect": r"fat: mounted /mnt/usb[\s\S]*fat-test: ok",
+     "expect": r"fat: mounted /volumes/usb[\s\S]*fat-test: ok",
      "fail":   r"DANOS-TEST-RESULT: FAIL"},
     # Phase 2b: mkdir/unlink through the mount. Reuses the fat-mount build — the
     # fat-test client, after listing, makes a directory, writes+reads a file inside
@@ -714,7 +714,7 @@ CASES = [
      "smp":    4,
      "timeout": 150,
      "qmp_after": {"delay": 8, "command": "system_powerdown"},
-     "expect": r"logger: logging to /var/log/\d{4}-\d{2}-\d{2}T\d{6}Z[\s\S]*"
+     "expect": r"logger: logging to /system/logs/\d{4}-\d{2}-\d{2}T\d{6}Z[\s\S]*"
                r"init: shutting down[\s\S]*"
                r"logger: flushed through sequence \d+[\s\S]*"
                r"power: entering S5",
@@ -935,7 +935,7 @@ def run_case(arch, case):
     # The bootable FAT32 USB image the build produced (tools/make-fat-image.py),
     # presented to the guest as a usb-storage device (see qemu_args).
     # Boot a per-run COPY of the image: the guest MUTATES its boot volume (the
-    # fat tests create/delete files; the logger writes /var/log), and QEMU is
+    # fat tests create/delete files; the logger writes /system/logs), and QEMU is
     # hard-killed after a match — booting the build artifact in place let one
     # run's leftovers fail the next (a stale TESTDIR trips the mkdir-duplicate
     # refusal) and dirtied the build cache's own output.