ci: Travis: no coverage by default [skip appveyor]

.travis.yml

@@ -12,15 +12,15 @@ install:
   - python -m pip install --upgrade --pre tox
 env:
   matrix:
-    - TOXENV=py27
+    - TOXENV=py27 PYTEST_COVERAGE=1
     # Specialized factors for py27.
-    - TOXENV=py27-nobyte
-    - TOXENV=py27-xdist
-    - TOXENV=py27-pluggymaster-xdist PYTEST_NO_COVERAGE=1
+    - TOXENV=py27-nobyte PYTEST_COVERAGE=1
+    - TOXENV=py27-xdist PYTEST_COVERAGE=1
+    - TOXENV=py27-pluggymaster-xdist
     # Specialized factors for py37.
     - TOXENV=py37-pexpect,py37-trial,py37-numpy
-    - TOXENV=py37-pluggymaster-xdist PYTEST_NO_COVERAGE=1
-    - TOXENV=py37-freeze PYTEST_NO_COVERAGE=1
+    - TOXENV=py37-pluggymaster-xdist
+    - TOXENV=py37-freeze
 
 matrix:
   allow_failures:
@@ -30,9 +30,9 @@ matrix:
 jobs:
   include:
     # Coverage tracking is slow with pypy, skip it.
-    - env: TOXENV=pypy-xdist PYTEST_NO_COVERAGE=1
+    - env: TOXENV=pypy-xdist
       python: 'pypy2.7-6.0'
-    - env: TOXENV=pypy3-xdist PYTEST_NO_COVERAGE=1
+    - env: TOXENV=pypy3-xdist
       python: 'pypy3.5-6.0'
 
     - env: TOXENV=py34-xdist
@@ -60,7 +60,7 @@ jobs:
         - test $(python -c 'import sys; print("%d%d" % sys.version_info[0:2])') = 37
 
     # Jobs only run via Travis cron jobs (currently daily).
-    - env: TOXENV=py38-xdist PYTEST_NO_COVERAGE=1
+    - env: TOXENV=py38-xdist
       python: '3.8-dev'
       if: type = cron
 
@@ -72,7 +72,6 @@ jobs:
 
     - stage: deploy
       python: '3.6'
-      env: PYTEST_NO_COVERAGE=1
       install: pip install -U setuptools setuptools_scm
       script: skip
       deploy:
@@ -88,7 +87,7 @@ jobs:
 
 before_script:
   - |
-    if [[ "$PYTEST_NO_COVERAGE" != 1 ]]; then
+    if [[ "$PYTEST_COVERAGE" = 1 ]]; then
       export COVERAGE_FILE="$PWD/.coverage"
       export COVERAGE_PROCESS_START="$PWD/.coveragerc"
       export _PYTEST_TOX_COVERAGE_RUN="coverage run -m"
@@ -99,7 +98,7 @@ script: tox --recreate
 
 after_success:
   - |
-    if [[ "$PYTEST_NO_COVERAGE" != 1 ]]; then
+    if [[ "$PYTEST_COVERAGE" = 1 ]]; then
       set -e
       # Add last TOXENV to $PATH.
       PATH="$PWD/.tox/${TOXENV##*,}/bin:$PATH"