`conjur init` respect ENV['CONJURRC'] now

Fixes for issue #69.

```
asakura@zen:~/tmp/cli-ruby$ CONJURRC=/tmp/test_env_rc conjur init
Enter the hostname (and optional port) of your Conjur endpoint: ec2-54-81-179-32.compute-1.amazonaws.com

SHA1 Fingerprint=74:E5:53:2A:4C:73:18:1B:7F:4A:AF:FD:6E:D9:9D:0D:05:17:44:C3

Please verify this certificate on the appliance using command:
                openssl x509 -fingerprint -noout -in ~conjur/etc/ssl/conjur.pem

Trust this certificate (yes/no): yes
Wrote certificate to /tmp/conjur-sandbox.pem
Wrote configuration to /tmp/test_env_rc
asakura@zen:~/tmp/cli-ruby$ cat /tmp/test_env_rc 
---
account: sandbox
plugins: []
appliance_url: https://ec2-54-81-179-32.compute-1.amazonaws.com/api
cert_file: "/tmp/conjur-sandbox.pem"
asakura@zen:~/tmp/cli-ruby$ cat /tmp/conjur-sandbox.pem | wc -l
20
```