update(notebooks, mfhob.py): clean paths in jupyter notebooks

[jlarsen-usgs]

• update export_utils.py to echo relative paths
• update export/utils.py to echo relative paths
• update echoed executable path in run_models
• update ModflowHob.load() to use flopy_io.line_strip()

[codecov]

Codecov Report

Merging #1711 (aeed97f) into develop (2552de5) will increase coverage by 0.0%.
The diff coverage is 100.0%.

@@           Coverage Diff           @@
##           develop   #1711   +/-   ##
=======================================
  Coverage     71.9%   71.9%           
=======================================
  Files          253     253           
  Lines        55891   55904   +13     
=======================================
+ Hits         40202   40219   +17     
+ Misses       15689   15685    -4     

Impacted Files	Coverage Δ
flopy/export/shapefile_utils.py	90.5% <100.0%> (ø)
flopy/export/utils.py	65.3% <100.0%> (-0.1%)	⬇️
flopy/mbase.py	69.1% <100.0%> (+<0.1%)	⬆️
flopy/modflow/mfhob.py	88.9% <100.0%> (+<0.1%)	⬆️
flopy/utils/check.py	75.7% <100.0%> (+<0.1%)	⬆️
flopy/utils/flopy_io.py	79.2% <100.0%> (+0.9%)	⬆️
flopy/utils/get_modflow.py	63.9% <0.0%> (+0.9%)	⬆️