ceph_argparse.cc: accept also 0/1 for boolean injectargs

Accept also 0 (as false) and 1 (true) as arguments for
boolean option on injectargs.

Fixes: #4261

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
Merge pull request #80 from dalgaaf/wip-da-4261

ceph_argparse.cc: accept also 0/1 for boolean injectargs

Reviewed-by: Sage Weil <sage@inktank.com>