TT#65907 Remove unnecessary subshell calls in helper build_config

It gives ~0.5 second better 'ngcpcfg apply' time.

Change-Id: Ib8d331b9b057708cc34106b82e05128a8019a44e

helper/build_config

@@ -46,6 +46,7 @@ if [ -n "${OUTPUT_DIRECTORY:-}" ] ; then
 else
   export output_file
 fi
+output_file_dirname="$(dirname "${output_file}")" # like /etc/mysql
 
 # ensure we don't try to generate a file where a directory with same name exists already
 if [ -d "${output_file}" ] ; then
@@ -57,15 +58,15 @@ fi
 if [ -r "${NGCPCTL_MAIN}/templates/${output_file}.prebuild" ] ; then
   log_info "Executing prebuild for ${output_file}"
   bash "${NGCPCTL_MAIN}/templates/${output_file}.prebuild"
-elif [ -r "${NGCPCTL_MAIN}/templates/$(dirname "${output_file}")/ngcpcfg.prebuild" ] ; then
+elif [ -r "${NGCPCTL_MAIN}/templates/${output_file_dirname}/ngcpcfg.prebuild" ] ; then
   log_info "Executing prebuild for ${output_file}"
-  bash "${NGCPCTL_MAIN}/templates/$(dirname "${output_file}")/ngcpcfg.prebuild"
+  bash "${NGCPCTL_MAIN}/templates/${output_file_dirname}/ngcpcfg.prebuild"
 fi
 
 # if output directory does not exist yet, create it
-if ! [ -d "$(dirname "${output_file}")" ] ; then
+if ! [ -d "${output_file_dirname}" ] ; then
   umask 0022 # directory permissions should be '755'
-  mkdir -p "$(dirname "${output_file}")"
+  mkdir -p "${output_file_dirname}"
 fi
 
 # assume safe defaults
@@ -144,9 +145,9 @@ fi
 if [ -r "${NGCPCTL_MAIN}/templates/${output_file}.postbuild" ] ; then
   log_info "Executing postbuild for ${output_file}"
   bash "${NGCPCTL_MAIN}/templates/${output_file}.postbuild"
-elif [ -r "${NGCPCTL_MAIN}/templates/$(dirname "${output_file}")/ngcpcfg.postbuild" ] ; then
+elif [ -r "${NGCPCTL_MAIN}/templates/${output_file_dirname}/ngcpcfg.postbuild" ] ; then
   log_info "Executing postbuild for ${output_file}"
-  bash "${NGCPCTL_MAIN}/templates/$(dirname "${output_file}")/ngcpcfg.postbuild"
+  bash "${NGCPCTL_MAIN}/templates/${output_file_dirname}/ngcpcfg.postbuild"
 fi
 
 exit $RC