Use tox for bashate testing

Create a tox.ini file to install bashate into a virtualenv for running
tests. It can be run with a command such as "tox -v -ebashate". The find
command being used is equivalent to the default list of files discovered
by bashate plus the exclusion of the .tox/ directory. Also add the .tox/
directory to the .gitignore file.

Change-Id: I94cab4e4a9118d62edfce29ead1f1e2a5f48e529

.gitignore

@@ -5,6 +5,7 @@
 *.pem
 .localrc.auto
 .prereqs
+.tox
 .stackenv
 accrc
 docs/files

tox.ini

@@ -0,0 +1,13 @@
+[tox]
+minversion = 1.6
+skipsdist = True
+envlist = bashate
+
+[testenv]
+usedevelop = False
+install_command = pip install {opts} {packages}
+
+[testenv:bashate]
+deps = bashate
+whitelist_externals = bash
+commands = bash -c "find {toxinidir} -not -wholename \*.tox/\* -and \( -name \*.sh -or -name \*rc -or -name functions\* -or \( -wholename lib/\* -and -not -name \*.md \) \) -print0 | xargs -0 bashate -v"