mon: Properly handle errors from 'cmd_getval()' when needed

Not handling the error return from cmd_getval() may leave uninitialzied
values, which can cause issues, specially with non-string values.

Fixes: 6806

Signed-off-by: Joao Eduardo Luis <joao.luis@inktank.com>
mon: Monitor: handle invalid 'quorum' command argument

Don't rely on client side validation of possible command arguments.

Signed-off-by: Joao Eduardo Luis <joao.luis@inktank.com>
mon: OSDMonitor: don't rely on client-side validation for command arguments

Signed-off-by: Joao Eduardo Luis <joao.luis@inktank.com>
Merge pull request #1490 from ceph/wip-6806

mon: Properly handle errors from 'cmd_getval()' when needed

Reviewed-by: Sage Weil <sage@inktank.com>