Add helpful log output to aid with troulbeshooting of vault login.

[damienjoldersma-rakuten]

I had some trouble with setting up Vault and Rundeck integration - I was receiving a NullPointerException in the logs with no other information to help me understand the problem of my misconfiguration.

This pull request will help others in troulbeshooting misconfiguration or other Vault / Rundeck integration problems. Basically it changes the plugin to not ignore and not to just swallow login exceptions.

Here are some example of the exception output that was being hidden, which were essential in understanding to resolve the misconfiguration:

[2024-03-11T02:07:26,527] WARN  vault-storage [qtp689905739-81] - Error logging into Vault: Encountered error while authenticating with approle: Vault responded with HTTP status code: 400
Response body: {"errors":["invalid role ID"]}

[2024-03-11T02:12:48,291] WARN  vault-storage [pool-12-thread-1] - Error logging into Vault: Encountered error while authenticating with approle: Vault responded with HTTP status code: 400
Response body: {"errors":["invalid secret id"]}