In order to reduce cardinality of the interrupts collector add
filtering options
* Add include/exclude regexp filter flags.
* Add boolean flag to include zero values, enabled by default.
Signed-off-by: Ben Kochie <superq@gmail.com>
Remove all hardcoded references to `/proc`. For all collectors that do
not use `github.com/prometheus/procfs` yet, provide a wrapper to
generate the full paths.
Reformulate help strings, errors and comments to remove absolute
references to `/proc`.
This is a breaking change: the `-collector.ipvs.procfs` flag is removed
in favor of the general flag. Since it only affected that collector it
was only useful for development, so this should not cause many issues.
