Remove quotes from subshell call in bash script

Always no quotes for $() statement.

We don't need quotes to hold blanks in result:
 # i=$(echo 1 2 3)
 # echo $i
 1 2 3
 #

These quotes can make something wrong in some case:
 # i=$(echo '!')
 #
 # i="$(echo '!')"
 -bash: !: event not found
 #

No real problem for current code, only to use a better code style.

Change-Id: If3a914650749d72c2eb13b9f1307ef7b4319bd2f
Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>

playbooks/roles/repo_server/files/openstack-wheel-builder.sh

@@ -97,7 +97,7 @@ function kill_job {
     set +e
     # If the job needs killing kill the pid and unlock the file.
     if [ -f "${LOCKFILE}" ]; then
-        PID="$(cat ${LOCKFILE})"
+        PID=$(cat ${LOCKFILE})
         lock_file_remove
         kill -9 "${PID}"
     fi

scripts/scripts-library.sh

@@ -31,7 +31,7 @@ FORKS=${FORKS:-$(grep -c ^processor /proc/cpuinfo)}
 function successerator {
   set +e
   # Get the time that the method was started.
-  OP_START_TIME="$(date +%s)"
+  OP_START_TIME=$(date +%s)
   RETRY=0
   # Set the initial return value to failure.
   false