#2132 - lint and fix with ale#command#Run

A new function is added here which will later be modified for public use
in linter and fixer callbacks. All linting and fixing now goes through
this new function, to prove that it works in all cases.

test/sign/test_linting_sets_signs.vader

@@ -63,5 +63,6 @@ After:
 
 Execute(The signs should be updated after linting is done):
   ALELint
+  call ale#test#FlushJobs()
 
   AssertEqual [['1', 'ALEWarningSign'], ['2', 'ALEErrorSign']], CollectSigns()

test/sign/test_sign_placement.vader

@@ -134,6 +134,7 @@ Given testft(A file with warnings/errors):
 
 Execute(The current signs should be set for running a job):
   ALELint
+  call ale#test#FlushJobs()
 
   AssertEqual
   \ [