mon/PGMap: restructure 'pg stat' formatted output

The + character, which appears in state names, is not a valid XML token.

Signed-off-by: Sage Weil <sage@redhat.com>
Merge pull request #3230 from ceph/wip-pg-stat

mon/PGMap: restructure 'pg stat' formatted output

Reviewed-by: John Spray <jspray@redhat.com>