Only expose a single namespace variable in Helm configuration

[venilnoronha]

Describe the bug As described in this comment, the Helm configuration currently accepts 2 namespace parameters as shown below.

https://github.com/vmware/wavefront-adapter-for-istio/blob/646ea4e89e711eea58e1ef0c1c0d7784deffa51f/install/wavefront/values.yaml#L15-L17

Currently, there's a bug in the adapter/Istio that causes the adapter to report no metrics when the entire Helm chart/yaml is deployed onto a single namespace other than istio-system.

Expected behavior We should accept only a single namespace parameter (instead of namespaces.istio and namespaces.adapter) and deploy everything from the Helm chart/yaml onto that namespace.

Steps to reproduce the bug Use the YAML configuration from the 0.1.0 or 0.1.1 versions of the adapter and update the namespace to something other than istio-system. You should see no metrics and logs flowing through the adapter.

[venilnoronha]

/cc @dlinsley