Unique resource name per resource class

[nlabriet]

Description
Allow using the same resource name across classes.
I tested it in my setup and created a test that fails without this fix.

Checklist

• Documentation for the feature
  • No documentation on this fix
• Tests for the feature
• PR has been tested

Fixes #1173

[codecov]

Codecov Report

Patch coverage: 100.0% and project coverage change: +0.2 🎉

Comparison is base (f6d02f2) 62.7% compared to head (1f0c904) 63.0%.

Additional details and impacted files

@@           Coverage Diff            @@
##           master   #1176     +/-   ##
========================================
+ Coverage    62.7%   63.0%   +0.2%     
========================================
  Files         159     159             
  Lines       11653   11653             
========================================
+ Hits         7312    7346     +34     
+ Misses       4341    4307     -34     

Impacted Files	Coverage Δ
labgrid/remote/client.py	51.3% <100.0%> (+1.8%)	⬆️
labgrid/resource/remote.py	82.5% <100.0%> (ø)

... and 2 files with indirect coverage changes

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[jluebbe]

Discussed this with @Emantor: While get_target_resources() returns a dict, we're never using it for lookups. So we should change this to a list or set of (resource_entry, name) tuples in the future.