sensors: raise only what the hardware says is failing, and say a hung watch

The review of #129 found false alarms and a silent failure: the NVMe temperature bit, old-age
attributes, a fan's minimum or latched alarm, an unrelated hot sensor and a board chip's limits could
raise a condition, while a hung smartctl stopped the fans' looks and an old readings file passed as
healthy. Read spinning drives hourly (smartd too) so a read never keeps one from spinning down, and skip
a drive that cannot say whether it sleeps.

modules/sensors/module.json

@@ -24,7 +24,7 @@
       "type": "file",
       "path": "/etc/smartd.conf",
       "mode": "0644",
-      "content": "# The mesh's (module sensors, novox/hq ADR 0256): what smartd watches. Written whole at every push;\n# an edit here is overwritten.\n#\n# Every drive smartd can find, with every check (-a). A drive in standby is skipped, never woken to be\n# checked, and the skip is not logged (-n standby,q): a server's spinning drives may sleep. No mail is\n# sent (no -m): what smartd finds goes to the journal, and the module's watch reads each drive's health\n# for the mesh's tools and its health check.\nDEVICESCAN -a -n standby,q\n"
+      "content": "# The mesh's (module sensors, novox/hq ADR 0256): what smartd watches. Written whole at every push;\n# an edit here is overwritten.\n#\n# Every drive smartd can find, with every check (-a). A drive in standby is skipped, never woken to be\n# checked, and the skip is not logged (-n standby,q): a server's spinning drives may sleep. A drive\n# behind a USB bridge that cannot say whether it is asleep is checked anyway by smartd, and may be woken\n# (novox/hq ADR 0256); the watch does not read such a drive. No mail is\n# sent (no -m): what smartd finds goes to the journal, and the module's watch reads each drive's health\n# for the mesh's tools and its health check.\nDEVICESCAN -a -n standby,q\n"
     },
     {
       "id": "smartd-drop-ins",
@@ -37,7 +37,7 @@
       "type": "file",
       "path": "/etc/systemd/system/smartd.service.d/10-mesh.conf",
       "mode": "0644",
-      "content": "# The mesh's (module sensors, novox/hq ADR 0256). Written whole at every push; edit nothing here.\n#\n# smartd runs on every machine the module is assigned to, a virtual machine included, where the package's\n# unit would not start; and it stays up on a machine with no drive it can watch (-q never), where it\n# would otherwise exit, because the mesh judges this service as one that stays up.\n[Unit]\nConditionVirtualization=\n\n[Service]\nExecStart=\nExecStart=/usr/bin/smartd -n -q never\n"
+      "content": "# The mesh's (module sensors, novox/hq ADR 0256). Written whole at every push; edit nothing here.\n#\n# smartd runs on every machine the module is assigned to, a virtual machine included, where the package's\n# unit would not start; and it stays up on a machine with no drive it can watch (-q never), where it\n# would otherwise exit, because the mesh judges this service as one that stays up. It checks each drive\n# hourly (-i 3600), not every half hour: a drive read more often than its standby timer never spins down,\n# and the module's watch reads a spinning drive hourly too.\n[Unit]\nConditionVirtualization=\n\n[Service]\nExecStart=\nExecStart=/usr/bin/smartd -n -q never -i 3600\n"
     },
     {
       "id": "smartd",