Refactor use of changedir in tox.ini (open-telemetry#3745)

Fixes open-telemetry#3744

tox.ini

@@ -96,29 +96,6 @@ setenv =
   CONTRIB_REPO=git+https://github.com/open-telemetry/opentelemetry-python-contrib.git@{env:CONTRIB_REPO_SHA}
   mypy: MYPYPATH={toxinidir}/opentelemetry-api/src/:{toxinidir}/tests/opentelemetry-test-utils/src/
 
-changedir =
-  api: opentelemetry-api/tests
-  sdk: opentelemetry-sdk/tests
-  protobuf: opentelemetry-proto/tests
-  semantic-conventions: opentelemetry-semantic-conventions/tests
-  getting-started: docs/getting_started/tests
-  opentracing-shim: shim/opentelemetry-opentracing-shim/tests
-  opencensus-shim: shim/opentelemetry-opencensus-shim/tests
-
-  exporter-opencensus: exporter/opentelemetry-exporter-opencensus/tests
-  exporter-otlp-proto-common: exporter/opentelemetry-exporter-otlp-proto-common/tests
-  exporter-otlp-combined: exporter/opentelemetry-exporter-otlp/tests
-  exporter-otlp-proto-grpc: exporter/opentelemetry-exporter-otlp-proto-grpc/tests
-  exporter-otlp-proto-http: exporter/opentelemetry-exporter-otlp-proto-http/tests
-  exporter-prometheus: exporter/opentelemetry-exporter-prometheus/tests
-  exporter-zipkin-combined: exporter/opentelemetry-exporter-zipkin/tests
-  exporter-zipkin-proto-http: exporter/opentelemetry-exporter-zipkin-proto-http/tests
-  exporter-zipkin-json: exporter/opentelemetry-exporter-zipkin-json/tests
-
-  propagator-b3: propagator/opentelemetry-propagator-b3/tests
-  propagator-jaeger: propagator/opentelemetry-propagator-jaeger/tests
-  test-utils: tests/opentelemetry-test-utils/tests
-
 commands_pre =
 ; Install without -e to test the actual installation
   py3{8,9,10,11}: python -m pip install -U pip setuptools wheel
@@ -128,7 +105,7 @@ commands_pre =
 
   protobuf: pip install {toxinidir}/opentelemetry-proto
 
-  getting-started: pip install -r requirements.txt
+  getting-started: pip install -r {toxinidir}/docs/getting_started/tests/requirements.txt
   getting-started: pip install -e {env:CONTRIB_REPO}\#egg=opentelemetry-util-http&subdirectory=util/opentelemetry-util-http
   getting-started: pip install -e {env:CONTRIB_REPO}\#egg=opentelemetry-instrumentation&subdirectory=opentelemetry-instrumentation
   getting-started: pip install -e {env:CONTRIB_REPO}\#egg=opentelemetry-instrumentation-requests&subdirectory=instrumentation/opentelemetry-instrumentation-requests
@@ -184,7 +161,28 @@ commands_pre =
   mypyinstalled: pip install file://{toxinidir}/opentelemetry-api/
 
 commands =
-  opentelemetry: pytest {posargs}
+  api: pytest {toxinidir}/opentelemetry-api/tests {posargs}
+  sdk: pytest {toxinidir}/opentelemetry-sdk/tests {posargs}
+  protobuf: pytest {toxinidir}/opentelemetry-proto/tests {posargs}
+  semantic-conventions: pytest {toxinidir}/opentelemetry-semantic-conventions/tests {posargs}
+  getting-started: pytest {toxinidir}/docs/getting_started/tests {posargs}
+  opentracing-shim: pytest {toxinidir}/shim/opentelemetry-opentracing-shim/tests {posargs}
+  opencensus-shim: pytest {toxinidir}/shim/opentelemetry-opencensus-shim/tests {posargs}
+
+  exporter-opencensus: pytest {toxinidir}/exporter/opentelemetry-exporter-opencensus/tests {posargs}
+  exporter-otlp-proto-common: pytest {toxinidir}/exporter/opentelemetry-exporter-otlp-proto-common/tests {posargs}
+  exporter-otlp-combined: pytest {toxinidir}/exporter/opentelemetry-exporter-otlp/tests {posargs}
+  exporter-otlp-proto-grpc: pytest {toxinidir}/exporter/opentelemetry-exporter-otlp-proto-grpc/tests {posargs}
+  exporter-otlp-proto-http: pytest {toxinidir}/exporter/opentelemetry-exporter-otlp-proto-http/tests {posargs}
+  exporter-prometheus: pytest {toxinidir}/exporter/opentelemetry-exporter-prometheus/tests {posargs}
+  exporter-zipkin-combined: pytest {toxinidir}/exporter/opentelemetry-exporter-zipkin/tests {posargs}
+  exporter-zipkin-proto-http: pytest {toxinidir}/exporter/opentelemetry-exporter-zipkin-proto-http/tests {posargs}
+  exporter-zipkin-json: pytest {toxinidir}/exporter/opentelemetry-exporter-zipkin-json/tests {posargs}
+
+  propagator-b3: pytest {toxinidir}/propagator/opentelemetry-propagator-b3/tests {posargs}
+  propagator-jaeger: pytest {toxinidir}/propagator/opentelemetry-propagator-jaeger/tests {posargs}
+  test-utils: pytest {toxinidir}/tests/opentelemetry-test-utils/tests {posargs}
+
   coverage: {toxinidir}/scripts/coverage.sh
 
   mypy: mypy --install-types --non-interactive --namespace-packages --explicit-package-bases opentelemetry-api/src/opentelemetry/