OSDMap: note encoding features in Incremental encoding

The monitor will need to know what features the incremental was encoded
with so that it can encode the OSDMap using the same bits.  Introduce a
member that is set during decode.  During encode, encoding the value passed
in by the caller.

Signed-off-by: Sage Weil <sage@inktank.com>
mon/OSDMonitor: encode full OSDMap with same feature bits as the Incremental

Each monitor is independently encoding the full OSDMap and storing it in
its local store.  Sometime this happens when we do not have a valid value
for quorum_features (for example, it can happen during sync).

Instead, use the feature bits the Incremental was encoded with for the full
OSDMap so that they always match.

Note that this conveniently the *only* place in the mon where we encode
the full OSDMap, so we're capturing all paths.  Yay!

Signed-off-by: Sage Weil <sage@inktank.com>
Merge pull request #1171 from ceph/wip-osdmap-features

mon: encode full osdmap with same feature bits as the incremental

Reviewed-by: Greg Farnum <greg@inktank.com>