Add a capability to guard riak_core_net_ticktime

The goal of this change is to prevent problems in a mixed version
cluster where the riak_core_net_ticktime module is not loaded. The
capability is net_ticktime and has two modes: supported and
unsupported. The supported mode is the preferred mode. The
net_ticktime daemon will not run until the capability has a mode of
supported.

This change also adds `riak_core_net_ticktime:enable/0` that can be
used to register the net_ticktime capability after the
riak_core_net_ticktime module is loaded on a node.
Only check capability on initial call to start_set_net_ticktime_daemon. Also change values of capability to boolean.
Add function to wrap capability check
Merge branch 'feature/net-ticktime-capability' into develop