Add option to disable/enable free disk space checking and percentage checking for full and not-full disks

Now the two option:

max-disk-utilization-per-disk-percentage
min-free-space-per-disk-mb

for full/not full disk check are all enabled always, i think it's more reasonable to enable or disable this, and default will be all enabled.

In our clusters, when the disk is so huge we want to use  min-free-space-per-disk-mb.

In our clusters,  when the disk is so small we want to use max-disk-utilization-per-disk-percentage.

We should make this more reasonable and not confused.

cc pbacsko  Jim_Brennan  ebadger  gandras