* 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* Fix out-of-date inline flag reference syntax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
* silently ignore nonexisting bonding_masters file
Add an empty fixtures dir without a bonding_masters file to test.
* Moved the check to the Update() method
Dropped the empty test dir.
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.
