silence new bandit warning

Test results:
>> Issue: [B507:ssh_no_host_key_verification] Paramiko call with policy set to automatically trust the unknown host key.
   Severity: High   Confidence: Medium
   CWE: CWE-295 (https://cwe.mitre.org/data/definitions/295.html)
   More Info: https://bandit.readthedocs.io/en/1.7.10/plugins/b507_ssh_no_host_key_verification.html
   Location: ./st2common/st2common/runners/paramiko_ssh.py:781:8
780             client = paramiko.SSHClient()
781             client.set_missing_host_key_policy(paramiko.AutoAddPolicy())
782

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Code scanned:
        Total lines of code: 21204
        Total lines skipped (#nosec): 0
        Total potential issues skipped due to specifically being disabled (e.g., #nosec BXXX): 0

Run metrics:
        Total issues (by severity):
                Undefined: 0
                Low: 15
                Medium: 13
                High: 1
        Total issues (by confidence):
                Undefined: 0
                Low: 3
                Medium: 13
                High: 13
Files skipped (0):

st2common/st2common/runners/paramiko_ssh.py

@@ -778,7 +778,8 @@ def _connect(self, host, socket=None):
             conninfo["sock"] = socket
 
         client = paramiko.SSHClient()
-        client.set_missing_host_key_policy(paramiko.AutoAddPolicy())
+        # FIXME: Allow the admin or end user control the host key policy
+        client.set_missing_host_key_policy(paramiko.AutoAddPolicy())  # nosec
 
         extra = {"_conninfo": conninfo}
         self.logger.debug("Connection info", extra=extra)