python/bandit: Use .bandit configuration file

Bandit automatically [uses any .bandit file] within the directories on
which it is invoked.  Since ALE invokes bandit on stdin, it does not
load a .bandit file automatically.  Add support for automatically
finding a .bandit file and passing it to bandit via the --ini option
along with a variable to disable this behavior if desired.

Note: This is useful for the skips and tests configuration options, but
not exclude which would require invoking bandit using a file name, which
may or may not be a good trade-off.

[uses any .bandit file]: https://github.com/PyCQA/bandit/blob/1.5.1/bandit/cli/main.py#L70-L73

Signed-off-by: Kevin Locke <kevin@kevinlocke.name>

ale_linters/python/bandit.vim

@@ -3,6 +3,7 @@
 
 call ale#Set('python_bandit_executable', 'bandit')
 call ale#Set('python_bandit_options', '')
+call ale#Set('python_bandit_use_config', 1)
 call ale#Set('python_bandit_use_global', get(g:, 'ale_use_global_executables', 0))
 call ale#Set('python_bandit_auto_pipenv', 0)
 
@@ -22,6 +23,14 @@ function! ale_linters#python#bandit#GetCommand(buffer) abort
     let l:flags = ' --format custom'
     \   . ' --msg-template "{line}:{test_id}:{severity}:{msg}" '
 
+    if ale#Var(a:buffer, 'python_bandit_use_config')
+        let l:config_path = ale#path#FindNearestFile(a:buffer, '.bandit')
+
+        if !empty(l:config_path)
+            let l:flags = ' --ini ' . ale#Escape(l:config_path) . l:flags
+        endif
+    endif
+
     let l:exec_args = l:executable =~? 'pipenv$'
     \   ? ' run bandit'
     \   : ''