Python release prep (#809)

* new recipe for new runtime

* add new runtime formula

* add test updates for new runtime release

* wrangle tests into submission

* update tests to use default_pythons

* delete commented code

test/fixtures/python2/runtime.txt

@@ -1 +1 @@
-python-2.7.15
+python-2.7.16

test/fixtures/python2_warn/runtime.txt

@@ -1 +1 @@
-python-2.7.14
+python-2.7.15

test/run

@@ -1,5 +1,9 @@
 #!/usr/bin/env bash
 
+# Default Python Versions
+# shellcheck source=bin/default_pythons
+source "$BIN_DIR/default_pythons"
+
 testAirflow() {
   export SLUGIFY_USES_TEXT_UNIDECODE="yes"
   compile "airflow"
@@ -19,13 +23,13 @@ testPipenvLock() {
 
 testPipenvVersion() {
   compile "pipenv-version"
-  assertCaptured "3.6.8"
+  assertCaptured $DEFAULT_PYTHON_VERSION
   assertCapturedSuccess
 }
 
 testPipenvVersion2() {
   compile "pipenv-version2"
-  assertCaptured "2.7.15"
+  assertCaptured $LATEST_27
   assertCapturedSuccess
 }
 testPipenvFullVersion() {
@@ -95,25 +99,21 @@ testPylibmc() {
 
 testPythonDefault() {
   compile "pythonDefault"
-  assertCaptured "python-3.6.8"
+  assertCaptured $DEFAULT_PYTHON_VERSION
   assertCapturedSuccess
 }
 
 testPython2() {
     compile "python2"
-    assertCaptured "python-2.7.15"
+    assertCaptured $LATEST_27
     assertCapturedSuccess
 }
 
 testPython2_warn() {
     compile "python2_warn"
-    if [[ $STACK = "heroku-18" ]]; then
-      assertCapturedError
-    else
-      assertCaptured "python-2.7.14"
-      assertCaptured "security update!"
-      assertCapturedSuccess
-    fi
+    assertCaptured "python-2.7.15"
+    assertCaptured "security update!"
+    assertCapturedSuccess
 }
 
 testPython2_fail() {
@@ -124,7 +124,7 @@ testPython2_fail() {
 
 testPython3_4() {
   compile "python3_4"
-  assertCaptured "python-3.4.9"
+  assertCaptured $LATEST_34
   assertCapturedSuccess
 }
 
@@ -147,7 +147,7 @@ testPython3_4_fail() {
 
 testPython3_5() {
   compile "python3_5"
-  assertCaptured "python-3.5.6"
+  assertCaptured $LATEST_35
   assertCapturedSuccess
 }
 
@@ -170,7 +170,7 @@ testPython3_5_fail() {
 
 testPython3_6() {
   compile "python3_6"
-  assertCaptured "python-3.6.8"
+  assertCaptured $LATEST_36
   assertCapturedSuccess
 }
 
@@ -192,7 +192,7 @@ testPython3_7() {
   if [[ $STACK = "cedar-14" ]]; then
     assertCapturedError
   else
-    assertCaptured "python-3.7.2"
+    assertCaptured $LATEST_37
     assertCapturedSuccess
   fi
 }