path.udev.data is not currently using the --path.rootfs prefix

[czephyr]

Currently when running the docker img you need to explicitly set the path.udev.data flag or it will run in:

level=error collector=diskstats msg="Failed to open directory, disabling udev device properties" path=/run/udev/data

the non-mounted location /run/udev/data is searched by default, when instead it should look in ${path.rootfs}/run/udev/data if --path.rootfs is set.

This is confusing because this flag is basically compulsory and is not well documented and doesn't align with the plug and play behavior of /procand/sys`.

This PR suggests to prepend the path.rootfs to the udev data path.
The drawback is that it might make setting --path.udev.data confusing if the user tries to already pass the prepended path like /host/run/udev/data but the error log in this case becomes helpful.

Testing

When running the current latest tag

docker run -d --net="host" --pid="host" -v "/:/host:ro,rslave" quay.io/prometheus/node-exporter:latest --path.rootfs=/host

ts=2024-12-23T22:00:48.494Z caller=node_exporter.go:193 level=info msg="Starting node_exporter" version="(version=1.8.2, branch=HEAD, revision=f1e0e8360aa60b6cb5e5cc1560bed348fc2c1895)"
ts=2024-12-23T22:00:48.494Z caller=node_exporter.go:194 level=info msg="Build context" build_context="(go=go1.22.5, platform=linux/amd64, user=root@03d440803209, date=20240714-11:53:45, tags=unknown)"
ts=2024-12-23T22:00:48.494Z caller=filesystem_common.go:111 level=info collector=filesystem msg="Parsed flag --collector.filesystem.mount-points-exclude" flag=^/(dev|proc|run/credentials/.+|sys|var/lib/docker/.+|var/lib/containers/storage/.+)($|/)
ts=2024-12-23T22:00:48.494Z caller=filesystem_common.go:113 level=info collector=filesystem msg="Parsed flag --collector.filesystem.fs-types-exclude" flag=^(autofs|binfmt_misc|bpf|cgroup2?|configfs|debugfs|devpts|devtmpfs|fusectl|hugetlbfs|iso9660|mqueue|nsfs|overlay|proc|procfs|pstore|rpc_pipefs|securityfs|selinuxfs|squashfs|sysfs|tracefs)$
ts=2024-12-23T22:00:48.494Z caller=diskstats_common.go:111 level=info collector=diskstats msg="Parsed flag --collector.diskstats.device-exclude" flag=^(z?ram|loop|fd|(h|s|v|xv)d[a-z]|nvme\d+n\d+p)\d+$
ts=2024-12-23T22:00:48.494Z caller=diskstats_linux.go:265 level=error collector=diskstats msg="Failed to open directory, disabling udev device properties" path=/run/udev/data
ts=2024-12-23T22:00:48.494Z caller=node_exporter.go:111 level=info msg="Enabled collectors"
ts=2024-12-23T22:00:48.494Z caller=node_exporter.go:118 level=info collector=arp
...
ts=2024-12-23T22:00:48.494Z caller=node_exporter.go:118 level=info collector=zfs
ts=2024-12-23T22:00:48.495Z caller=tls_config.go:313 level=info msg="Listening on" address=[::]:9100
ts=2024-12-23T22:00:48.495Z caller=tls_config.go:316 level=info msg="TLS is disabled." http2=false address=[::]:9100

When running the local image built from branch
docker run -d --net="host" --pid="host" -v "/:/host:ro,rslave" node_exporter_local --path.rootfs=/host

time=2024-12-23T21:57:58.938Z level=INFO source=node_exporter.go:216 msg="Starting node_exporter" version="(version=1.8.1, branch=udev_path_flag, revision=e22301c0dd1779dbee2e70c33982354a427e348e)"
time=2024-12-23T21:57:58.938Z level=INFO source=node_exporter.go:217 msg="Build context" build_context="(go=go1.23.3, platform=linux/amd64, user=alfredo@alfredo-x1, date=20241223-21:49:52, tags=unknown)"
time=2024-12-23T21:57:58.938Z level=INFO source=filesystem_common.go:250 msg="Parsed flag --collector.filesystem.mount-points-exclude" collector=filesystem flag=^/(dev|proc|run/credentials/.+|sys|var/lib/docker/.+|var/lib/containers/storage/.+)($|/)
time=2024-12-23T21:57:58.938Z level=INFO source=filesystem_common.go:279 msg="Parsed flag --collector.filesystem.fs-types-exclude" collector=filesystem flag=^(autofs|binfmt_misc|bpf|cgroup2?|configfs|debugfs|devpts|devtmpfs|fusectl|hugetlbfs|iso9660|mqueue|nsfs|overlay|proc|procfs|pstore|rpc_pipefs|securityfs|selinuxfs|squashfs|sysfs|tracefs)$
time=2024-12-23T21:57:58.939Z level=INFO source=diskstats_common.go:110 msg="Parsed flag --collector.diskstats.device-exclude" collector=diskstats flag=^(z?ram|loop|fd|(h|s|v|xv)d[a-z]|nvme\d+n\d+p)\d+$
time=2024-12-23T21:57:58.939Z level=INFO source=node_exporter.go:135 msg="Enabled collectors"
time=2024-12-23T21:57:58.939Z level=INFO source=node_exporter.go:141 msg=arp
...
time=2024-12-23T21:57:58.939Z level=INFO source=node_exporter.go:141 msg=zfs
time=2024-12-23T21:57:58.939Z level=INFO source=tls_config.go:347 msg="Listening on" address=[::]:9100
time=2024-12-23T21:57:58.939Z level=INFO source=tls_config.go:350 msg="TLS is disabled." http2=false address=[::]:9100

[czephyr]

needs tests to be adapted