Cache manager has no test coverage

[evan2645]

The cache manager has no test coverage and is a little hard to read. Refactor cache manager as necessary, and ensure test coverage is above 80%.

[evan2645]

Just listing a few recently-fixed bugs here so we can be sure to include test cases for them:
SVID is cached immediately on manager start (in case of agent restart before SVID rotation)
Subscribers get up-to-date bundle
Manager survives CA rotation