LU-14948 build: Warn about /usr/src/lustre.tar.bz2

LU-14948 build: Warn about /usr/src/lustre.tar.bz2

When /usr/src/lustre.tar.bz2 exists, make debs (and dkms-debs)
will fail with an error like:

  Extracting the package tarball, /usr/src/lustre.tar.bz2, ...
  ../../generic.sh: line 73: debian/rules: Permission denied
  BUILD FAILED!

Add the current git hash to the lustre tarball, as well as
attempt to remove the conflict from /usr/src.  Failing that,
give a warning to ask the user to remove the conflicting file.

Lustre-change: https://review.whamcloud.com/44677
Lustre-commit: 1d97ac16d8ade4786202c2e9005896a2ac661340

HPE-bug-id: LUS-10308
Test-Parameters: trivial
Signed-off-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Change-Id: I4aaa803cb81c2ed8ffc0182bb49ea0bff5064df4
Reviewed-on: https://review.whamcloud.com/47775
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>