ipmi_sensor does not correctly parse negative values

[tarrychk]

ipmi_sensor plugin with metric version 2 does not parse negative values in the description field correctly:

# ipmitool sdr elist
[...]
DIMM Thrm Mrgn 1 | B0h | ok  |  8.1 | -55 degrees C
DIMM Thrm Mrgn 2 | B1h | ok  |  8.2 | -55 degrees C
DIMM Thrm Mrgn 3 | B2h | ok  |  8.3 | -53 degrees C
DIMM Thrm Mrgn 4 | B3h | ok  |  8.4 | -57 degrees C
[...]

Relevant telegraf.conf:

[[inputs.ipmi_sensor]]
  interval = "120s"
  timeout = "20s"
  metric_version = 2

System info:

telegraf v1.14.2
Ubuntu 18.04
ipmitool 1.8.18-5ubuntu0.1

Steps to reproduce:

1. Configure ipmi_sensor plugin on a host where ipmitool supports sensor values that yield negative values.

Expected behavior:

ipmi_sensor plugin should convert
DIMM Thrm Mrgn 1 | B0h | ok | 8.1 | -55 degrees C
to
ipmi_sensor,entity_id=8.1,status_code=ok,unit=degrees_c dimm_thrm_mrgn_1=-55 1588753149000000000

Actual behavior:

DIMM Thrm Mrgn 1 | B0h | ok | 8.1 | -55 degrees C
gets converted to
ipmi_sensor,entity_id=8.1,status_code=ok,status_desc=-55_degrees_c dimm_thrm_mrgn_1=0 1588753050000000000

Additional info:

I found that patching re_v2_parse_description regexp in ipmi.go to allow an optional minus-sign before the analog value resolves the issue for me.

diff --git a/plugins/inputs/ipmi_sensor/ipmi.go b/plugins/inputs/ipmi_sensor/ipmi.go
index 9ac842b8..fb53e1bc 100644
--- a/plugins/inputs/ipmi_sensor/ipmi.go
+++ b/plugins/inputs/ipmi_sensor/ipmi.go
@@ -21,7 +21,7 @@ var (
        execCommand             = exec.Command // execCommand is used to mock commands in tests.
        re_v1_parse_line        = regexp.MustCompile(`^(?P<name>[^|]*)\|(?P<description>[^|]*)\|(?P<status_code>.*)`)
        re_v2_parse_line        = regexp.MustCompile(`^(?P<name>[^|]*)\|[^|]+\|(?P<status_code>[^|]*)\|(?P<entity_id>[^|]*)\|(?:(?P<description>[^|]+))?`)
-       re_v2_parse_description = regexp.MustCompile(`^(?P<analogValue>[0-9.]+)\s(?P<analogUnit>.*)|(?P<status>.+)|^$`)
+       re_v2_parse_description = regexp.MustCompile(`^(?P<analogValue>-?[0-9.]+)\s(?P<analogUnit>.*)|(?P<status>.+)|^$`)
        re_v2_parse_unit        = regexp.MustCompile(`^(?P<realAnalogUnit>[^,]+)(?:,\s*(?P<statusDesc>.*))?`)
 )

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