Re-Executing GRID setup fails with [FATAL] [INS-30024]

Re-Executing GRID setup fails with [FATAL] [INS-30024]

After an unclean deinstallation gridSetup.sh fails with error  [FATAL] [INS-30024]
Instead of offering the option to install a NEW cluster the installer offers the GRID Upgrade option

Debugging with strace

[grid@dsctw21 grid]$   gridSetup.sh -silent  -skipPrereqs -responseFile  /home/grid/grid_dsctw2.rsp    oracle.install.asm.SYSASMPassword=sys    oracle.install.asm.monitorPassword=sys 2>llog2
Launching Oracle Grid Infrastructure Setup Wizard...

[FATAL] [INS-30024] Installer has detected that the location determined as Oracle Grid Infrastructure home (/u01/app/122/grid), is not a valid Oracle home.
   ACTION: Ensure that either there are no environment variables pointing to this invalid location or register the location as an Oracle home in the central inventory.

Using strace to trace system calls 
[grid@dsctw21 grid]$ strace -f  gridSetup.sh -silent  -skipPrereqs -responseFile  /home/grid/grid_dsctw2.rsp    oracle.install.asm.SYSASMPassword=sys    oracle.install.asm.monitorPassword=sys 2>llog
Launching Oracle Grid Infrastructure Setup Wizard...

[FATAL] [INS-30024] Installer has detected that the location determined as Oracle Grid Infrastructure home (/u01/app/122/grid), is not a valid Oracle home.
   ACTION: Ensure that either there are no environment variables pointing to this invalid location or register the location as an Oracle home in the central inventory.

Check Log File for failed open calls or for open calls which  should fail in CLEAN Installation ENV 
grid@dsctw21 grid]$ grep open llog
..
[pid 11525] open("/etc/oracle/ocr.loc", O_RDONLY) = 93
[pid 11525] open("/etc/oracle/ocr.loc", O_RDONLY) = 93

--> It seems the installer is testing for files
 /etc/oracle/ocr.loc
 /etc/oracle/olr.loc 
whether its an upgrade or its a new installation. 

Fix : Rename ocr.log and olr.loc 
[root@dsctw21 ~]# mv /etc/oracle/ocr.loc /etc/oracle/ocr.loc_tbd
[root@dsctw21 ~]# mv /etc/oracle/olr.loc /etc/oracle/olr.loc_tbd

Now gridSetup.sh should start the installation process