scripts/pkgdep: Disable mdl installation on centos

Versions of centos we support - 7 and 8 - don't ship with ruby which
can handle installation of the mdl gem due to unmet dependencies -
it's simply too old.

Signed-off-by: Michal Berger <michalx.berger@intel.com>
Change-Id: Id0a3843bcab12b8de332d1d3f64956f043c347e3
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/9483
Community-CI: Mellanox Build Bot
Community-CI: Broadcom CI <spdk-ci.pdl@broadcom.com>
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Ben Walker <benjamin.walker@intel.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>
Reviewed-by: Monica Kenguva <monica.kenguva@intel.com>
Reviewed-by: Karol Latecki <karol.latecki@intel.com>

scripts/pkgdep/common.sh

@@ -109,7 +109,11 @@ install_markdownlint() {
 if [[ $INSTALL_DEV_TOOLS == true ]]; then
 	install_shfmt
 	install_spdk_bash_completion
-	install_markdownlint
+	if [[ $ID != centos ]]; then
+		install_markdownlint
+	else
+		echo "mdl not supported on $ID, disabling"
+	fi
 fi
 
 if [[ $INSTALL_LIBURING == true ]]; then