BIGTOP-3266: Rat check failed for one file with unapproved/unknown licenses
BIGTOP-3266: Rat check failed for one file with unapproved/unknown licenses

Add .dockerignore to Rat exclude-file list.

Change-Id: Ia4a052db2df7d1e8e87bcde3304ea401a706759b
Signed-off-by: Yuqi Gu <345a4e3af047c06b177f7fe1915a45f6033d9349@arm.com>

apache/bigtop,JunHe77/bigtop,JunHe77/bigtop,sekikn/bigtop,apache/bigtop,JunHe77/bigtop,JunHe77/bigtop,sekikn/bigtop,apache/bigtop,apache/bigtop,sekikn/bigtop,sekikn/bigtop,sekikn/bigtop,apache/bigtop