use env vars instead of hardcoded paths

Author: bofm

step1/install.sh

@@ -5,4 +5,4 @@ trap "echo '******* Caught SIGINT signal. Stopping...'; exit 2" SIGINT
 
 gosu oracle /bin/bash -c "cd /tmp/install/database/ && ./runInstaller -waitforcompletion -ignoreSysPrereqs -ignorePrereq -silent -noconfig -responseFile /tmp/install/db_install.rsp" &
 wait $!
-/app/oracle/product/12.1.0/dbhome_1/root.sh
+$ORACLE_HOME/root.sh