Test for exception on non-HTTP healthcheck URI

Add a spec test to expect an exception when a healthcheck URI is set on
a healthcheck using a protocol other than HTTP.

This test currently fails; the next commit will make it run
successfully.
Don't set healthcheck URI for non-HTTP checks

Don't set a healthcheck URI for non-HTTP load balancer healthchecks.

In vCloud Director version 5.1 and 5.5, VMWare does not support a
healthcheck URI for SSL healthchecks[1]. In vCloud Director version 5.5,
a load balancer will refuse connections if a health check URL is set for
an SSL healthcheck.

TCP healthchecks obviously would not use a HTTP URI given they do not
operate at layer 7.

Also, raise an exception if a healthcheck URI is specified for a load
balancer healthcheck using any protocol other than HTTP.

This corresponds to similar changes in the 'vcloud-edge_gateway' gem
which is designed to replace 'vcloud-net-spinner'[2].

Note that vcloud-net-spinner doesn't currently support TCP load
balancers, so we only raise an exception for SSL healthchecks.

[1]:
http://pubs.vmware.com/vcd-55/topic/com.vmware.vcloud.admin.doc_55/GUID-C12B3954-155F-48AF-9855-E0DE026752D0.html
[2]:
https://github.com/alphagov/vcloud-edge_gateway/commit/ecfba3960d8ae44169af81afd36647926226de15
Version 0.2.0

Bump version to 0.2.0 and update CHANGELOG to include changes for
load balancer healthcheck URIs.

Bump the major version rather than the minor as the exception raised for
some healthcheck URIs may break some configurations if a healthcheck URI
has been set for an SSL healthcheck.