vstart.sh: -e to create an ec pool called 'ec'

Signed-off-by: Sage Weil <sage@inktank.com>
mon: right justify df values

Signed-off-by: Sage Weil <sage@inktank.com>
mon: include 'max avail' in df output

Include an estimate of the maximum writeable space for each pool.  Note
that this value is a conservative estimate for that pool based on the
most-full OSD.  It is also potentially misleading as it is the available
space if *all* new data were written to this pool; one cannot (generally)
add up the available space for all pools.

Signed-off-by: Sage Weil <sage@inktank.com>
mon: set min_size to data chunk count for erasure pools

This makes the k and k+m values both readily available from pg_pool_t
without making others parse the erasure profile.  This is useful for making
the smart df output, among other things.

Signed-off-by: Sage Weil <sage@inktank.com>