analyze: clear all figures after running each followup

This makes sure we're not holding up figures (and consuming memory)
unnecessarily.

locklost/analyze.py

@@ -3,6 +3,8 @@ import sys
 import argparse
 import logging
 
+from matplotlib import pyplot as plt
+
 from . import __version__, set_signal_handlers
 from . import config
 from .plugins import FOLLOWUPS
@@ -62,6 +64,7 @@ def analyze_event(event, plugins=None):
         except:
             complete = False
             logging.exception("exception in {}:".format(name))
+        plt.close('all')
 
     if complete:
         logging.info("analysis complete")