sleep within exception hanlder

Change-Id: Ic6919d00ac0af9ea13307274486f48c48243287a
migrate to JSON configs

Change-Id: I7aae0a661f045864cf8718b1bc4b1f6cf1ef8480
allow to restrict list of buckets and nodes

Optionally it's possible to restrict list of buckets and hostnames
used for stats collection via "buckets" and "hostnames" directives:

    "buckets": ["bucket-1"]
    "hostnames": []

Empty list will disallow stats collection for given domain
(bucket/server).

Change-Id: Ic1bc64777cb7f56c52b6de521ef5d87c36c670ac