Attempt to build an allowed failure mechanism

And use it to let the PyPy job fail.

.circleci/config.yml

@@ -93,6 +93,10 @@ jobs:
         user: "nobody"
 
     environment: &UTF_8_ENVIRONMENT
+      # In general, the test suite is not allowed to fail while the job
+      # succeeds.  But you can set this to "yes" if you want it to be
+      # otherwise.
+      ALLOWED_FAILURE: "no"
       # Tell Hypothesis which configuration we want it to use.
       TAHOE_LAFS_HYPOTHESIS_PROFILE: "ci"
       # Tell the C runtime things about character encoding (mainly to do with
@@ -131,6 +135,7 @@ jobs:
             /tmp/project/.circleci/run-tests.sh \
                 "/tmp/venv" \
                 "/tmp/project" \
+                "${ALLOWED_FAILURE}" \
                 "${ARTIFACTS_OUTPUT_PATH}" \
                 "${TAHOE_LAFS_TOX_ENVIRONMENT}" \
                 "${TAHOE_LAFS_TOX_ARGS}"
@@ -174,6 +179,7 @@ jobs:
     environment:
       <<: *UTF_8_ENVIRONMENT
       TAHOE_LAFS_TOX_ENVIRONMENT: "pypy27-coverage"
+      ALLOWED_FAILURE: "yes"
 
 
   c-locale:

.circleci/run-tests.sh

@@ -13,6 +13,9 @@ shift
 PROJECT_ROOT="$1"
 shift
 
+ALLOWED_FAILURE="$1"
+shift
+
 ARTIFACTS=$1
 shift
 
@@ -54,11 +57,16 @@ export SUBUNITREPORTER_OUTPUT_PATH="${SUBUNIT2}"
 export TAHOE_LAFS_TRIAL_ARGS="--reporter=subunitv2-file --rterrors"
 export PIP_NO_INDEX="1"
 
+if [ "${ALLOWED_FAILURE}" = "yes" ]; then
+    alternative = "true"
+else
+    alternative = "false"
+
 ${BOOTSTRAP_VENV}/bin/tox \
     -c ${PROJECT_ROOT}/tox.ini \
     --workdir /tmp/tahoe-lafs.tox \
     -e "${TAHOE_LAFS_TOX_ENVIRONMENT}" \
-    ${TAHOE_LAFS_TOX_ARGS}
+    ${TAHOE_LAFS_TOX_ARGS} || "${alternative}"
 
 if [ -n "${ARTIFACTS}" ]; then
     # Create a junitxml results area.