FAB-15675 Fix issues flagged by shellcheck

For check_license.sh & metrics_doc.sh
Need to check with shellcheck 0.6.0

Change-Id: I39c60cf4a9326e9fa5f74159a9f9a199bb77d1fe
Signed-off-by: Atsushi Neki <atsushin@fast.au.fujitsu.com>

Author: nekia

scripts/check_license.sh

@@ -5,7 +5,8 @@
 # SPDX-License-Identifier: Apache-2.0
 #
 
-source "$(cd $(dirname "$0") && pwd)/functions.sh"
+# shellcheck source=/dev/null
+source "$(cd "$(dirname "$0")" && pwd)/functions.sh"
 
 CHECK=$(git diff --name-only --diff-filter=ACMRTUXB HEAD | tr '\n' ' ')
 if [[ -z "$CHECK" ]]; then

scripts/metrics_doc.sh

@@ -14,7 +14,7 @@ case "$1" in
     # check if the metrics documentation is up to date with the metrics
     # options in the tree
     "check")
-        if [ -n "$(diff -u <(cd ${fabric_dir} && ${gendoc_command}) ${metrics_doc})" ]; then
+        if [ -n "$(diff -u <(cd "${fabric_dir}" && ${gendoc_command}) "${metrics_doc}")" ]; then
             echo "The Fabric metrics reference documentation is out of date."
             echo "Please run '$0 generate' to update the documentation."
             exit 1
@@ -23,7 +23,7 @@ case "$1" in
 
     # generate the metrics documentation
     "generate")
-         (cd "${fabric_dir}" && ${gendoc_command} > ${metrics_doc})
+         (cd "${fabric_dir}" && ${gendoc_command} > "${metrics_doc}")
         ;;
 
     *)