LU-12033 build: Git ignore generated *.install files

LU-12033 build: Git ignore generated *.install files

Building client or server DEB packages generates files:
* lustre-server-utils.install
* lustre-client-utils.install
from description files
* lustre-server-utils.install.in
* lustre-client-utils.install.in
Any modifications take place in *.install.in files,
thus gitignore the generated *.install files.

Test-Parameters: trivial
Signed-off-by: Thomas Stibor <t.stibor@gsi.de>
Change-Id: Ib7812f3407b35a74ef8bd63e630bda24fcbd5b48
Reviewed-on: https://review.whamcloud.com/34344
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Nathaniel Clark <nclark@whamcloud.com>