Add Swift MaaS healthchecks.

* Add Check for local swift-proxy-server
* Add Check for local swift-container-server
* Add Check for local swift-object-server
* Add Check for local swift-account-server
* Add Check for remote swift-proxy-server

All checks are GET requests against /healthcheck with ane expected
response of 200 OK.

Fixes: #396
Merge pull request #397 from andymcc/swift_maas

Add Swift MaaS healthchecks.