* Move NodeCollector into package collector
* Refactor collector enabling
* Update README with new collector enabled flags
* Fix out-of-date inline flag reference syntax
* Use new flags in end-to-end tests
* Add flag to disable all default collectors
* Track if a flag has been set explicitly
* Add --collectors.disable-defaults to README
* Revert disable-defaults flag
* Shorten flags
* Fixup timex collector registration
* Fix end-to-end tests
* Change procfs and sysfs path flags
* Fix review comments
* Add metrics from SNTPv4 packet to ntp collector & add ntpd sanity check
1. Checking local clock against remote NTP daemon is bad idea, local
ntpd acting as a client should do it better and avoid excessive load on
remote NTP server so the collector is refactored to query local NTP
server.
2. Checking local clock against remote one does not check local ntpd
itself. Local ntpd may be down or out of sync due to network issues, but
clock will be OK.
3. Checking NTP server using sanity of it's response is tricky and
depends on ntpd implementation, that's why common `node_ntp_sanity`
variable is exported.
* `govendor add golang.org/x/net/ipv4`, it is dependency of github.com/beevik/ntp
* Update github.com/beevik/ntp to include boring SNTP fix
* Use variable name from RFC5905
* ntp: move code to make export of raw metrics more explicit
* Move NTP math to `github.com/beevik/ntp`
* Make `golint` happy
* Add some brief docs explaining `ntp` #655 and `timex` #664 modules
* ntp: drop XXX comment that got its decision
* ntp: add `_seconds` suffix to relevant metrics
* Better `node_ntp_leap` comment
* s/node_ntp_reftime/node_ntp_reference_timestamp_seconds/ as requested by @discordianfish
* Extract subsystem name to const as suggested by @SuperQ
Named return variables should only be used to describe the returned type
further, e.g. `err error` doesn't add any new information and is just
stutter.
Previously the raw time difference was used which includes the network trip time
between the node and the ntp server. This makes setting alerts off the value
troublesome as it depends on the latency as well as the clock offset.
This puts all collector-specific flags into their own namespace under
"collector.<collector-name>", and moves from camel case to dashes, which
is the standard in Prometheus land now.
Switch to Update using the Collecter Collect interface, due to not knowing all
metricnames in all modules beforehand we can't use Describe and thus the full
Collecter interface.
Remove 'updates', it's meaning varies by module and doesn't add much.
