modetest: print more about our properties

In the future we'll have more than just connector properties, so create
a dump_prop function that can handle any property (instead of the
current dump_props function that only handles connector properties).

Also, make this function print a lot more information about the existing
properties.

Also change the printed indentation of the modes to make the output more
readable.

The previous function dump_props also segfaulted when we didn't have
enought permissions. The new function does not segfault in this case (by
checking for the return value of drmModeGetProperty).

Reviewed-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>