Tolerate missing deps in get-stats.py

In order to run on systems where not all requirements are present,
we should be tolerant of missing external dependencies, such as
psutil and pymysql. Print a warning (to stderr) and just leave out
those stats in that case.

Also make running the stats collector use ignore_errors:yes to avoid
failures in the future. I think the stats is not critical enough to
fail a job for bugs like this.

Related-Bug: #1970195
Change-Id: I132b0e1f5033c4f109a8b8cc776c0877574c4a49

roles/capture-performance-data/tasks/main.yaml

@@ -13,3 +13,4 @@
       {% for i in debian_suse_apache_deref_logs.results | default([]) + redhat_apache_deref_logs.results | default([]) %}
       --apache-log="{{ i.stat.path }}"
       {% endfor %}
+  ignore_errors: yes

tools/get-stats.py

@@ -6,12 +6,24 @@ import glob
 import itertools
 import json
 import os
-import psutil
 import re
 import socket
 import subprocess
 import sys
-import pymysql
+
+try:
+    import psutil
+except ImportError:
+    psutil = None
+    print('No psutil, process information will not be included',
+          file=sys.stderr)
+
+try:
+    import pymysql
+except ImportError:
+    pymysql = None
+    print('No pymysql, database information will not be included',
+          file=sys.stderr)
 
 # https://www.elastic.co/blog/found-crash-elasticsearch#mapping-explosion
 
@@ -144,10 +156,10 @@ if __name__ == '__main__':
 
     data = {
         'services': get_services_stats(),
-        'db': args.db_pass and get_db_stats(args.db_host,
-                                            args.db_user,
-                                            args.db_pass) or [],
-        'processes': get_processes_stats(args.process),
+        'db': pymysql and args.db_pass and get_db_stats(args.db_host,
+                                                        args.db_user,
+                                                        args.db_pass) or [],
+        'processes': psutil and get_processes_stats(args.process) or [],
         'api': get_http_stats(args.apache_log),
         'report': get_report_info(),
     }