Add logical drive capacity to metrics collection

[ibrahimkk-moideen]

Code test:

=== RUN   Test_Exporter_Metrics_Handling
=== RUN   Test_Exporter_Metrics_Handling/Good_Logical_Drive
--- PASS: Test_Exporter_Metrics_Handling (0.00s)
    --- PASS: Test_Exporter_Metrics_Handling/Good_Logical_Drive (0.00s)
PASS
ok  	github.com/comcast/fishymetrics/exporter	0.265s

Test result:

# HELP redfish_logical_drive_status Current Logical Drive Raid 1 = OK, 0 = BAD, -1 = DISABLED
# TYPE redfish_logical_drive_status gauge
redfish_logical_drive_status{capacityMiB="285568",chassisModel="dl365",chassisSerialNumber="xxxxxxx",logicaldrivename="",name="MR Volume",raid="RAID1",volumeuniqueidentifier="600062B2152120802C3301EEB844E987"} 1

[derrick-dacosta]

LGTM