Consul cloud auto join secrets wrong interpretation with Azure generated secret

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#### Overview of the Issue

With consul cloud auto join providers if we pass secret contains "$!" interprets as number. added single quote for secret as per https://www.consul.io/docs/agent/cloud-auto-join.html but still Azure login fails.

#### Reproduction Steps

Steps to reproduce this issue, eg:

1. Create a cluster with 3 server nodes in azure VM.
2. Use azure service principle generated contains characters "$!" for cloud auto join.
3. View error in consul monitor

### Consul info for Server

Consul version: 1.7.2