Add support for multiple tags and host labels for cloud auto-join

#### Feature Description

The cloud auto-join feature would really benefit from supporting setting multiple tags and host labels to allow for more fine-grained filtering of the nodes to auto-join to.

#### Use Case(s)

Lets say I have multiple clusters (A,B,C) deployed in the same GCE project, all the consul servers in those clusters are tagged with "auto-join" to easily targeting them with the retry_join setting.

However the problem now is that if I try to auto-join using
```
"retry_join": ["provider=gce project_name=myProject tag_value=auto-join"]
```
I will get all the nodes from clusters A,B and C, since all the servers have the tag, but I only want nodes from one of them.

**Proposed solution**
Support for setting filter for host labels multiple tags :
```
"retry_join": ["provider=gce project_name=myProject tag_value=auto-join tag_value=uniqueTag label=uniqueLabel"]
```
This would enable filtering out nodes among multiple clusters that have the same 'auto-join' tag.