Add unit tests for host instrumentation

[Petrie]

Resolve https://github.com/open-telemetry/opentelemetry-go-contrib/issues/2755

[codecov[bot]]

Codecov Report

Merging #3517 (980873e) into main (83a9d91) will increase coverage by 1.9%. The diff coverage is 100.0%.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #3517     +/-   ##
=======================================
+ Coverage   69.9%   71.9%   +1.9%     
=======================================
  Files        147     147             
  Lines       6934    6934             
=======================================
+ Hits        4851    4988    +137     
+ Misses      1959    1807    -152     
- Partials     124     139     +15     

Impacted Files	Coverage Δ
instrumentation/host/host.go	76.2% <100.0%> (+76.2%)	:arrow_up:

... and 2 files with indirect coverage changes

[dmathieu]

Adding tests shouldn't need a changelog entry. Also, what is preventing those tests from residing in the same package as the code?

[Petrie]

@dmathieu

1. change log will be removed
2. By adding these tests to a separate test sub-directory, we can avoid unnecessary dependencies on the metric SDK in the host directory.

[pellared]

@Petrie, are you still willing to work on this?