Add bandit linter for Python

test/command_callback/test_bandit_command_callback.vader

@@ -0,0 +1,49 @@
+Before:
+  call ale#assert#SetUpLinterTest('python', 'bandit')
+  let b:bandit_flags = ' --format custom '
+  \   . '--msg-template "{line}:{test_id}:{severity}:{msg}" '
+
+After:
+  call ale#assert#TearDownLinterTest()
+  unlet! b:bandit_flags
+
+Execute(The bandit command callback should return default string):
+  AssertLinter 'bandit',
+  \ ale#Escape('bandit')
+  \ . b:bandit_flags
+  \ . ' -'
+
+Execute(The bandit command callback should allow options):
+  let g:ale_python_bandit_options = '--configfile bandit.yaml'
+
+  AssertLinter 'bandit',
+  \ ale#Escape('bandit')
+  \ . b:bandit_flags
+  \ . ' --configfile bandit.yaml -'
+
+Execute(The bandit executable should be configurable):
+  let g:ale_python_bandit_executable = '~/.local/bin/bandit'
+
+  AssertLinter '~/.local/bin/bandit',
+  \ ale#Escape('~/.local/bin/bandit')
+  \ . b:bandit_flags
+  \ . ' -'
+
+Execute(Setting executable to 'pipenv' appends 'run bandit'):
+  let g:ale_python_bandit_executable = 'path/to/pipenv'
+
+  AssertLinter 'path/to/pipenv',
+  \ ale#Escape('path/to/pipenv')
+  \ . ' run bandit'
+  \ . b:bandit_flags
+  \ . ' -'
+
+Execute(Pipenv is detected when python_bandit_auto_pipenv is set):
+  let g:ale_python_bandit_auto_pipenv = 1
+  call ale#test#SetFilename('/testplugin/test/python_fixtures/pipenv/whatever.py')
+
+  AssertLinter 'pipenv',
+  \ ale#Escape('pipenv')
+  \ . ' run bandit'
+  \ . b:bandit_flags
+  \ . ' -'