Optionally use RUNAS_GID to runas command to set group to setregid() to.

This is needed to prevent errors such as:
  mds blocked setgid attempt (1000/1000 -> 100)

lustre/tests/replay-sanity.sh

@@ -102,7 +102,11 @@ if [ $UID -ne 0 ]; then
         RUNAS=""
 else
         RUNAS_ID=${RUNAS_ID:-500}
-        RUNAS=${RUNAS:-"runas -u $RUNAS_ID"}
+        if [ -z "$RUNAS_GID" ]; then
+	    RUNAS=${RUNAS:-"runas -u $RUNAS_ID"}
+        else
+	    RUNAS=${RUNAS:-"runas -u $RUNAS_ID -g $RUNAS_GID"}
+        fi
 fi
 
 OLDTMPDIR=$TMPDIR

lustre/tests/sanity.sh

@@ -58,7 +58,11 @@ if [ $UID -ne 0 ]; then
 	RUNAS=""
 else
 	RUNAS_ID=${RUNAS_ID:-500}
-	RUNAS=${RUNAS:-"runas -u $RUNAS_ID"}
+        if [ -z "$RUNAS_GID" ]; then
+	    RUNAS=${RUNAS:-"runas -u $RUNAS_ID"}
+        else
+	    RUNAS=${RUNAS:-"runas -u $RUNAS_ID -g $RUNAS_GID"}
+        fi
 fi
 
 if [ `using_krb5_sec $SECURITY` == 'y' ] ; then

lustre/tests/sanityN.sh

@@ -31,7 +31,11 @@ if [ $UID -ne 0 ]; then
 	RUNAS=""
 else
 	RUNAS_ID=${RUNAS_ID:-500}
-	RUNAS=${RUNAS:-"runas -u $RUNAS_ID"}
+        if [ -z "$RUNAS_GID" ]; then
+	    RUNAS=${RUNAS:-"runas -u $RUNAS_ID"}
+        else
+	    RUNAS=${RUNAS:-"runas -u $RUNAS_ID -g $RUNAS_GID"}
+        fi
 fi
 
 if [ `using_krb5_sec $SECURITY` == 'y' ] ; then