Regex in rule definition doesn't like escaped dots

SUMMARY

An escaped dot \. regex pattern within a rule definition throws an error when registering the pack.

ISSUE TYPE

Bug Report

STACKSTORM VERSION

Paste the output of st2 3.0.1, on Python 2.7.6:

OS / ENVIRONMENT / INSTALL METHOD

Ubuntu 14.04 Docker Container. The pack was both installed as python2 and using the python3 option.

STEPS TO REPRODUCE

1. Create a new rules with the criterea

  trigger.action_ref:
    type: "regex"
    pattern: "[^(.*\.create_alert|.*\.process-failed-job|ostk_deploy\..*|ostk_auto_approve\..*)]"

2. Register the pack
   st2 pack register [pack]

EXPECTED RESULTS

I expect the pack to register.

ACTUAL RESULTS

# st2 pack register ostk_common
ERROR: 400 Client Error: Bad Request
MESSAGE: Failed to register rule "/opt/stackstorm/packs.dev/ostk_common/rules/failed-job-monitor-v2.yaml" from pack "ostk_common": while scanning a double-quoted scalar
  in "/opt/stackstorm/packs.dev/ostk_common/rules/failed-job-monitor-v2.yaml", line 19, column 14
found unknown escape character '.'
  in "/opt/stackstorm/packs.dev/ostk_common/rules/failed-job-monitor-v2.yaml", line 19, column 21 for url: http://127.0.0.1:9101/v1/packs/register

Removing the escaped dot \. allows the pack to register.

Start with the failing rules/failed-job-monitor-v2.yaml example and reproduce the error using st2 pack register [pack]. Trace the rule-registration path that parses the pattern, then verify that escaped dots are accepted and that registration succeeds without regressing other rule definitions.