FIX: missing keys should not cause failure in backend

[klauer]

Description

Missing keys should not cause a find match to fail.

Motivation and Context

Investigating xcs long load times

2022-03-03 16:44:27 - PID 7917         json_db.py: 149 _iterative_compare DEBUG    - Comparison method failed: 'lightpath'
Traceback (most recent call last):
  File "/u1/xcsopr/conda_envs/pcds-5.2.1/lib/python3.9/site-packages/happi/backends/json_db.py", line 146, in _iterative_compare
    if comparison(name, doc):
  File "/u1/xcsopr/conda_envs/pcds-5.2.1/lib/python3.9/site-packages/happi/backends/json_db.py", line 190, in comparison
    if all(value == doc[k] for k, value in to_match.items()):
  File "/u1/xcsopr/conda_envs/pcds-5.2.1/lib/python3.9/site-packages/happi/backends/json_db.py", line 190, in <genexpr>
    if all(value == doc[k] for k, value in to_match.items()):
KeyError: 'lightpath'

[tangkong]

This all looks good to me, though it doesn't seem to help my load times. I'm getting significantly longer load times than the scientists mentioned (~1.5 min), so I should look into that.

These changes are still good though

[klauer]

Yeah, @tangkong, this was more "unnecessary log spam" than anything.
I'm relatively certain that speed issue is due to the reasons listed in #235 - I think it'd be good to come up with a consensus on what's an acceptable solution there.

[ZLLentz]

Retroactive LGTM