[sonic_installer] should not return fail (rc=1) if new image is the same as what has been installed

[maggiemsft]

sonic_installer return 1 if the upgrade new image is the same as what has been installed

Steps to reproduce the issue

1. use sonic_installer to upgrade SONiC to same image version

Describe the results you received
shell returns 1 which indicate fail

Describe the results you expected
could it exit with success while do not do "reinstall"?

Additional information you deem important (e.g. issue happens only occasionally)

Output of show version

(paste your output here)

[jleveque]

Root cause of nonzero exit code is in sonic-buildimage/installer/x86_64/install.sh.

PR to fix this is at: sonic-net/sonic-buildimage#1389