df output can wrap breaking the disk space checks

[michaelsembwever]

The output of df can wrap over multiple lines if device names are long. This breaks the disk space checks here and here.

For example

$ df -h /tmp/datastax
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/vg_root-lv_tmp
                      6.0G  761M  4.9G  14% /tmp

The use of df's --portability option could be helpful, but it is not available on macos.

[michaelsembwever]

being worked on in https://github.com/datastax/diagnostic-collection/pull/111