bash string comparison fixes for cvmfs server scripts

cvmfs/server/cvmfs_server_json.sh

@@ -91,7 +91,7 @@ _render_info_file() {
     echo '  "last_geodb_update" : "'$modtime'",'
   fi
 
-  if [ "x${CVMFS_PUBLISH_VERSIONS_IN_META_FILE}" == "xtrue" ]; then
+  if [ "x${CVMFS_PUBLISH_VERSIONS_IN_META_FILE}" = "xtrue" ]; then
     echo '  "cvmfs_version" : "'$(cvmfs_version_string)'",'
     echo '  "os_id" : "'$(_os_id)'", '
     echo '  "os_version_id" : "'$(_os_version_id)'", '

cvmfs/server/cvmfs_server_util.sh

@@ -757,11 +757,11 @@ _os_etc_release_get_field() {
   _os_set_etc_release_filename
 
   local fieldname=$1
-  if [ "x${fieldname}" == "x" ]; then
+  if [ "x${fieldname}" = "x" ]; then
     die "Internal error: _os_etc_release_get_field expects a field name to search for!"
   fi
 
-  if [ "x${_CVMFS_OS_RELEASE_FILENAME}" == "x" ]; then
+  if [ "x${_CVMFS_OS_RELEASE_FILENAME}" = "x" ]; then
     # If we are unable to find a proper /etc/os-release file return nothing.
     :
   else