vmagent metric_relabel_configs affect automatically generated timeseries

[weenxin]

Describe the bug
According prometheus document ,

Metric relabeling does not apply to automatically generated timeseries such as up.

To Reproduce
some config with metric_relabel_configs with keep action(not include up metrics).

Expected behavior
the up metrics should not be removed.

Version

$ ./victoria-metrics-prod --version
vmagent-20200628-065703-heads-master-0-g05d754d-dirty-ff8a2fbe

Used command-line flags

bin/vmagent  \
-httpListenAddr=:8429 \
-memory.allowedPercent=70  \
-maxInsertRequestSize=1024000000 \
-promscrape.config=bin/prometheus.yaml \
-promscrape.maxScrapeSize=10240000000 \
-promscrape.configCheckInterval=1m \
-remoteWrite.tmpDataPath=data \
-remoteWrite.queues=50 \
-remoteWrite.maxBlockSize=1024000000 \
-remoteWrite.flushInterval=10s \
-remoteWrite.url=http://host1:8480/insert/1128/prometheus/api/v1/write  \
-remoteWrite.url=http://host2:8480/insert/1128/prometheus/api/v1/write  \
-remoteWrite.url=http://host3:8480/insert/1128/prometheus/api/v1/write  \
-remoteWrite.url=http://host4:8480/insert/1128/prometheus/api/v1/write

[valyala]

The issue should be fixed in the commit 1cd01b5 . Leaving the issue open until the bugfix is included in the next release.

[valyala]

The bugfix has been included in v1.37.4. Closing the issue as fixed.