df plugin does not handle df_complex vs df_inodes difference

[tgharold]

In collectd 5.3, the df plugin creates (2) sets of files. One is prefixed with "df_complex" the other is prefixed with "df_inodes" (created by "ReportInodes true" setting).

CGP displays both of these as "Free space (device-name)" in the graph headers and uses "Bytes" as the Y-axis label on both. The inodes chart needs to have the y-axis changed and the graph title changed.

Sample filenames:

df_complex-free.rrd
df_complex-reserved.rrd
df_complex-used.rrd
df_inodes-free.rrd
df_inodes-reserved.rrd
df_inodes-used.rrd