Require a KubeletClient in master.New().

Without this, tests which create a master
will panic with a nil pointer when the periodic
podCache update runs.

Deleted unused FakePodInfoGetter.
Added FakeKubeletClient.
Passed to master.New.
Required a KubeletClient in master.New.
Merge pull request #2142 from erictune/fix_crash

Require a KubeletClient in master.New()