mon: add key[=value] ... to osd pool create

With the introduction of the erasure code pool, arguments to be
interpreted depending on the pool type must be introduced.
For instance the erasure code pool loads a plugin at run time will
use easure-code-k=10 to split each object in 10.

The arguments are described as

  name=properties,type=CephString,n=N,req=false,goodchars=[A-Za-z0-9-_.=]

If key=value it is stored in the new properties data member of pg_pool_t
as properties[key] = value, otherwise the value is the empty string.

The pg_pool_t version is bumped to 10 and the encode/decode methods
modified to take the properties into account. The
generate_test_instances method creates a two entries map, one of which
is the empty string to cover the case when no value is specified.

http://tracker.ceph.com/issues/6113 refs #6113

Signed-off-by: Loic Dachary <loic@dachary.org>
Merge pull request #578 from dachary/wip-6113

mon: add key[=value] ... to osd pool create

Reviewed-by: Sage Weil <sage@inktank.com>