Use make automatic variables to install updated manuals

Make will choose modified manual from build directory or original from source
directory automagically. Take advantage of install tool feature.
Install all files in single command instead of iterating on each of them.

(cherry picked from commit 88f913ac)
13 jobs for modified-manual-install-oot-v9_12 in 7 minutes and 7 seconds (queued for 6 seconds)
Status Job ID Name Coverage
  Precheck
passed precheck:debian:sid:amd64 #29520
amd64 docker linux

00:00:13

 
  Build
passed build:centos:centos6:amd64 #29521
amd64 docker linux

00:01:59

passed build:centos:centos7:amd64 #29522
amd64 docker linux

00:02:07

passed build:debian:sid:amd64 #29523
amd64 docker linux

00:01:33

passed build:debian:sid:i386 #29524
i386 docker linux

00:01:26

 
  Test
passed systemtest:centos:centos6:amd64 #29529
amd64 docker linux

00:04:38

passed systemtest:centos:centos7:amd64 #29530
amd64 docker linux

00:04:42

passed systemtest:debian:sid:amd64 #29531
amd64 docker linux

00:04:39

passed systemtest:debian:sid:i386 #29532
i386 docker linux

00:04:44

passed unittest:centos:centos6:amd64 #29525
amd64 docker linux

00:00:54

passed unittest:centos:centos7:amd64 #29526
amd64 docker linux

00:00:54

passed unittest:debian:sid:amd64 #29527
amd64 docker linux

00:00:43

passed unittest:debian:sid:i386 #29528
i386 docker linux

00:00:47