opentracing-shim: add testbed for otshim (#727)

This commit ports the OpenTracing testbed[1] to check that the ot-shim is
working as expected using different frameworks.

Gevent doesn't support context vars yet[2], so those tests are not compatible
with opentelemetry and were not ported.

[1] https://github.com/opentracing/opentracing-python/tree/master/testbed
[2] https://github.com/gevent/gevent/issues/1407

Co-authored-by: Mauricio Vásquez <mauricio@kinvolk.io>
Co-authored-by: alrex <aboten@lightstep.com>

scripts/coverage.sh

@@ -3,13 +3,25 @@
 set -e
 
 function cov {
-    pytest \
-        --ignore-glob=*/setup.py \
-        --cov ${1} \
-        --cov-append \
-        --cov-branch \
-        --cov-report='' \
-        ${1}
+    if [ ${TOX_ENV_NAME:0:4} == "py34" ]
+    then
+        pytest \
+            --ignore-glob=*/setup.py \
+            --ignore-glob=ext/opentelemetry-ext-opentracing-shim/tests/testbed/* \
+            --cov ${1} \
+            --cov-append \
+            --cov-branch \
+            --cov-report='' \
+            ${1}
+    else
+        pytest \
+            --ignore-glob=*/setup.py \
+            --cov ${1} \
+            --cov-append \
+            --cov-branch \
+            --cov-report='' \
+            ${1}
+    fi
 }
 
 PYTHON_VERSION=$(python -c 'import sys; print(".".join(map(str, sys.version_info[:3])))')