destination: add constant to verify destination

certificate by default.

sbws/globals.py

@@ -53,6 +53,8 @@ MAX_BW_DIFF_PERC = 50
 
 BW_LINE_SIZE = 510
 
+DESTINATION_VERIFY_CERTIFICATE = True
+
 
 def fail_hard(*a, **kw):
     ''' Log something ... and then exit as fast as possible '''

sbws/lib/destination.py

@@ -6,6 +6,8 @@ from threading import RLock
 import requests
 from urllib.parse import urlparse
 from stem.control import EventType
+
+from sbws.globals import DESTINATION_VERIFY_CERTIFICATE
 import sbws.util.stem as stem_utils
 import sbws.util.requests as requests_utils
 
@@ -14,7 +16,7 @@ log = logging.getLogger(__name__)
 
 def _parse_verify_option(conf_section):
     if 'verify' not in conf_section:
-        return True
+        return DESTINATION_VERIFY_CERTIFICATE
     try:
         return conf_section.getboolean('verify')
     except ValueError: