autotools plugin: Dont regenerate existing configure scripts

This closes #256
11 jobs for master in 28 minutes and 45 seconds (queued for 4 seconds)
Status Job ID Name Coverage
  Prepare
passed #73709834
source_dist

00:00:28

 
  Test
passed #73709839
docs

00:00:37

passed #73709835
tests-debian-8

00:25:19

passed #73709836
tests-debian-9

00:25:11

passed #73709837
tests-fedora-27

00:13:07

passed #73709838
tests-unix

00:11:03

 
  Post
passed #73709841
analysis

00:00:35

passed #73709840
allowed to fail
codequality

00:02:56

passed #73709842
coverage

00:00:27

84.71%
passed #73709843
pages

00:00:18

 
  Deploy
passed pages:deploy

00:00:07