Fixing get_rule_file_hash to always return bytes

[JeffAshton]

Description

Fixing get_rule_file_hash for the case where an import is changed or removed, and the cached import path no longer exists. get_rule_file_hash will now always return bytes.

"Job "Internal: Handle Config Change (trigger: interval[0:02:30], next run at: 2021-11-19 21:05:16 UTC)" raised an exception
Traceback (most recent call last):
  File "/usr/local/lib/python3.10/site-packages/apscheduler/executors/base.py", line 125, in run_job
    retval = job.func(*job.args, **job.kwargs)
  File "/usr/local/lib/python3.10/site-packages/elastalert/elastalert.py", line 1312, in handle_config_change
    self.load_rule_changes()
  File "/usr/local/lib/python3.10/site-packages/elastalert/elastalert.py", line 1128, in load_rule_changes
    new_rule_hashes = self.rules_loader.get_hashes(self.conf, self.args.rule)
  File "/usr/local/lib/python3.10/site-packages/elastalert/loaders.py", line 577, in get_hashes
    rule_mod_times[rule_file] = self.get_rule_file_hash(rule_file)
  File "/usr/local/lib/python3.10/site-packages/elastalert/loaders.py", line 610, in get_rule_file_hash
    rule_file_hash += self.get_rule_file_hash(import_rule_file)
TypeError: can't concat str to bytes"

Checklist

• I have reviewed the contributing guidelines.
• I have included unit tests for my changes or additions.
• I have successfully run make test-docker with my changes.
• I have manually tested all relevant modes of the change in this PR.
• I have updated the documentation.
• I have updated the changelog.

Comments

RulesLoader should really be immutable. The fact that it's stateful and caches import_rules is sketchy for updates.

[JeffAshton]

Was returning string when file not found, which when concatenated with bytes in the case of import rules,

elastalert2/elastalert/loaders.py

Line 613 in caa0de3

rule_file_hash += self.get_rule_file_hash(import_rule_file)

throws TypeError: can't concat str to bytes

[jertel]

Thanks!