HYD-4698 fix prepare-commit-msg warning
HYD-4698 fix prepare-commit-msg warning

In HYD-3860 a warning was added to the commit hook if one
was modifying chroma-externals. The annoying part is that
this warning messes up commit messages even on rebases.
This fixes that.

Signed-off-by: Brian J. Murrell <2a8f564cbb80211e19c0a14fed38a451599c042f@intel.com>
Change-Id: I8de00f006982411d2f0a79046f6e09cefd4dbac3
Reviewed-on: http://review.whamcloud.com/16047
Tested-by: Jenkins
Tested-by: Chroma Test User <a0b98b2ff5154776fa24760ef410655af7a8b56c@intel.com>
Reviewed-by: Chris Gearing <149a3c4298d99c315fc555357d57d2940923ba5f@intel.com>

intel-hpdd/intel-manager-for-lustre,intel-hpdd/intel-manager-for-lustre,intel-hpdd/intel-manager-for-lustre