dbus-sdr: Make VoltageRegulatorMode exposed to sensorTree.

getSensorSubtree() now search for
xyz.openbmc_project.Control.VoltageRegulatorMode
under the path /xyz/openbmc_project/vr.

Only the failure of searching sensor path is considered as an error.

Tested: ipmiStorageGetSDR()

This requires all the changes in
https://gerrit.openbmc-project.xyz/q/hashtag:%22dbus-sdr-vr-sensors%22+(status:open%20OR%20status:merged)

```
ipmitool sdr list event -v
Running Get PICMG Properties my_addr 0x20, transit 0, target 0
Error response 0xc1 from Get PICMG Properities
Running Get VSO Capabilities my_addr 0x20, transit 0, target 0
Invalid completion code received: Invalid command
Discovered IPMB address 0x0
Sensor ID              : vr_sensor_0_fprof (0xb4)
Entity ID              : 11.5 (Add-in Card)
Sensor Type            : Module / Board (0x15)

Sensor ID              : vr_sensor_1_fprof (0xb5)
Entity ID              : 11.6 (Add-in Card)
Sensor Type            : Module / Board (0x15)

...

```

Signed-off-by: Hao Jiang <jianghao@google.com>
Change-Id: I76d3fedb1cc0a2bc865c2a9c83c0418eb0ee99be
Signed-off-by: Willy Tu <wltu@google.com>
2 files changed