Simplify Sauce Labs credential configs (#383)

Jenkinsfile

@@ -24,7 +24,7 @@ pipeline {
       "--variables=capabilities.json " +
       "--variables=${VARIABLES}"
     PULSE = credentials('PULSE')
-    SAUCELABS_API_KEY = credentials('SAUCELABS_API_KEY')
+    SAUCELABS = credentials('SAUCELABS')
   }
   stages {
     stage('Lint') {

tox.ini

@@ -4,8 +4,8 @@ envlist = py27, flake8
 
 [testenv]
 passenv = BUILD_NUMBER DISPLAY GIT_BRANCH GIT_COMMIT GIT_URL JENKINS_URL \
-    JOB_NAME PYTEST_ADDOPTS PYTEST_BASE_URL SAUCELABS_API_KEY \
-    SAUCELABS_USERNAME
+    JOB_NAME PYTEST_ADDOPTS PYTEST_BASE_URL SAUCELABS_USR \
+    SAUCELABS_PSW
 deps = -rrequirements/tests.txt
 commands = pytest \
     --html=results/{envname}.html --self-contained-html \