Add validation leeway_seconds on riak-cs-admin gc batch <leeway_seconds> [JIRA: RCS-239]

[ksauzz]

riak-cs-admin gc batch passes leeway_secounds argument to riak_cs_gc_d and let a process crash.

2015-07-14 08:55:32.982 [error] <0.8038.0> CRASH REPORT Process riak_cs_gc_d with 1 neighbours exited with reason: bad arithmetic expression in riak_cs_gc_key_list:fetch_eligible_manifest_keys/4 line 89 in gen_fsm:terminate/7 line 622
2015-07-14 08:55:32.983 [error] <0.145.0> Supervisor riak_cs_sup had child riak_cs_gc_d started with riak_cs_gc_d:start_link() at <0.8038.0> exit with reason bad arithmetic expression in riak_cs_gc_key_list:fetch_eligible_manifest_keys/4 line 89 in context child_terminated

[kuenishi]

Which version of Riak CS are you referring? Is that 2.0?

[ksauzz]

It's Riak CS 2.0.1.