MNT: shutter check and sim_db name

[chiahaoliu]

1. Use np.allclose to check shutter readback value, instead of strict equality
2. Standardizing name of simulated db path

[codecov-io]

Codecov Report

Merging #40 into master will decrease coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #40      +/-   ##
==========================================
- Coverage   98.42%   98.41%   -0.02%     
==========================================
  Files           7        7              
  Lines         127      126       -1     
==========================================
- Hits          125      124       -1     
  Misses          2        2

Impacted Files	Coverage Δ
xpdsim/area_det.py	100% <100%> (ø)	⬆️
xpdsim/tests/conftest.py	100% <100%> (ø)	⬆️

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