No error is reported when user queries file is not valid

[ikorolev93]

https://github.com/wrouesnel/postgres_exporter/blob/aeec47ead4ad3941cf1b6588b1ac5a44ca9e9c4b/cmd/postgres_exporter/postgres_exporter.go#L542-L546

Not sure if it's supposed to return err and log it somewhere else, or return nil and log it right here, since it is being ignored otherwise.

[patsevanton]

/usr/bin/postgres_exporter --version
postgres_exporter v0.8.0 (built with go1.11)

DATA_SOURCE_NAME="user=postgres host=/var/run/postgresql/ sslmode=disable" /usr/bin/postgres_exporter --extend.query-path=/etc/prometheus/postgres_exporter_queries.yaml --log.level="debug"
INFO[0000] Established new database connection to "/var/run/postgresql/:5432".  source="postgres_exporter.go:878"
DEBU[0000] Querying Postgres Version on "/var/run/postgresql/:5432"  source="postgres_exporter.go:1388"
INFO[0000] Semantic Version Changed on "/var/run/postgresql/:5432": 0.0.0 -> 9.6.15  source="postgres_exporter.go:1405"
DEBU[0000] flush_lsn is being forced to discard due to version incompatibility.  source="postgres_exporter.go:596"
DEBU[0000] pg_current_wal_lsn_bytes is being forced to discard due to version incompatibility.  source="postgres_exporter.go:596"
DEBU[0000] pg_current_wal_lsn is being forced to discard due to version incompatibility.  source="postgres_exporter.go:596"
DEBU[0000] sent_lsn is being forced to discard due to version incompatibility.  source="postgres_exporter.go:596"
DEBU[0000] write_lag is being forced to discard due to version incompatibility.  source="postgres_exporter.go:596"
DEBU[0000] write_lsn is being forced to discard due to version incompatibility.  source="postgres_exporter.go:596"
DEBU[0000] procpid is being forced to discard due to version incompatibility.  source="postgres_exporter.go:596"
DEBU[0000] replay_lsn is being forced to discard due to version incompatibility.  source="postgres_exporter.go:596"
DEBU[0000] pg_wal_lsn_diff is being forced to discard due to version incompatibility.  source="postgres_exporter.go:596"
DEBU[0000] flush_lag is being forced to discard due to version incompatibility.  source="postgres_exporter.go:596"
DEBU[0000] replay_lag is being forced to discard due to version incompatibility.  source="postgres_exporter.go:596"

[patsevanton]

Fixed in https://github.com/wrouesnel/postgres_exporter/pull/362/files