Make schema validation optional

There are a lot of issues, so we're only partially validating the spec
now. We still validate with prance, but skip checking x-api-model
because there are so many legacy issues.

I looked at adding the x-api-model ... but wow, we haven't been adding
that for a long time. And there are open issues about it:
#3575
#3788

So, we just make it possible, but optional, to run the schema validation.

st2common/st2common/cmd/validate_api_spec.py

@@ -45,6 +45,14 @@
     )
 )
 
+# When disabled, only load the spec in prance to validate. Otherwise check for x-api-model as well.
+# validate-defs is disabled by default until these are resolved:
+#   https://github.com/StackStorm/st2/issues/3575
+#   https://github.com/StackStorm/st2/issues/3788
+cfg.CONF.register_cli_opt(
+    cfg.BoolOpt("validate-defs", short="-d", required=False, default=False)
+)
+
 cfg.CONF.register_cli_opt(
     cfg.BoolOpt("generate", short="-c", required=False, default=False)
 )
@@ -71,6 +79,7 @@ def _validate_definitions(spec):
 
             if verbose:
                 LOG.info("Supplied definition for model %s: \n\n%s.", model, definition)
+                msg += "\n"
 
             error = True
             LOG.error(msg)
@@ -81,6 +90,7 @@ def _validate_definitions(spec):
 def validate_spec():
     spec_file = cfg.CONF.spec_file
     generate_spec = cfg.CONF.generate
+    validate_defs = cfg.CONF.validate_defs
 
     if not os.path.exists(spec_file) and not generate_spec:
         msg = (
@@ -103,10 +113,13 @@ def validate_spec():
     parser = prance.ResolvingParser(spec_file)
     spec = parser.specification
 
+    if not validate_defs:
+        return True
+
     return _validate_definitions(spec)
 
 
-def teartown():
+def teardown():
     common_teardown()
 
 
@@ -119,11 +132,13 @@ def main():
         spec_loader.load_spec("st2common", "openapi.yaml.j2")
 
         # run the schema through prance to validate openapi spec.
-        ret = validate_spec()
+        passed = validate_spec()
+
+        ret = 0 if passed else 1
     except Exception:
         LOG.error("Failed to validate openapi.yaml file", exc_info=True)
         ret = 1
     finally:
-        teartown()
+        teardown()
 
     return ret