Add new tox environment with Swift master branch

This is prep for making new testing environment with
master branch of Swift. Currently, we tests just for stable
version because Swift master branch doesn't care our third
party middleware. However, Swift3 seems being major stuff
for some companies.

In my consideration, I hope this tox will be just a notification
(i.e. non-voting) for Swift and Swift3 when making a new patch.

Change-Id: I4c667a56967f10d4c129fbd8165372b0976fa853

tox.ini

@@ -37,6 +37,14 @@ commands = /bin/bash {posargs:swift3/test/functional/run_test.sh}
 setenv = AUTH=tempauth
          S3ACL=true
 
+[testenv:s3acl_master]
+commands = /bin/bash {posargs:swift3/test/functional/run_test.sh}
+setenv = AUTH=tempauth
+         S3ACL=true
+deps =
+  -r{toxinidir}/test-requirements.txt
+  git+git://github.com/openstack/swift.git
+
 [testenv:pylint]
 # Avoid to fail by checking members at lxml dynamically loaded module
 commands = pylint -E swift3 --ignored-modules=lxml.etree