bench init with preferred Python EXEC for CI (#13336)

* bench_init.sh added python executable flag for environment setup

* Added future python build matrix

* udpate build matrix

* Update .travis.yml

* Update .travis.yml

.travis.yml

@@ -3,6 +3,11 @@ dist: trusty
 
 python:
   - "2.7"
+  - "3.6"
+  
+ matrix:
+  - allow_failures:
+    - python: "3.6"
 
 services:
   - mysql

travis/bench_init.sh

@@ -4,5 +4,5 @@ cd ~/
 curl -I https://github.com/frappe/frappe/tree/$TRAVIS_BRANCH | head -n 1 | cut -d $' ' -f2 | (
 	read response;
 	[ $response == '200' ] && branch=$TRAVIS_BRANCH || branch='develop';
-	bench init frappe-bench --frappe-path https://github.com/frappe/frappe.git --frappe-branch $branch
+	bench init frappe-bench --frappe-path https://github.com/frappe/frappe.git --frappe-branch $branch --python $(which python)
 )