Enhanced sdp_upgrade.sh to work with both the new Package Structure
/opt/perforce/helix-sdp and the legacy SDP structure when doing
upgrades of /p4/common and /p4/sdp. If the Package Structure
is already used, this will continue using it. If the legacy
strucutre is in use, it will continue using that. As the
helix-sdp package is not yet available, the Package Structure
will exist only if the new install_sdp.sh script was used
for the install (or if the customer is one of a few early
adopters of the new structure).
This version, to be released with SDP 2024.2, will NOT migrate from
the legacy structure to the Package structure. Doing so requires
running as root; that change is targeted for release in SDP 2025.1.
Also removed the dependency on perl from sdp_upgrade.sh.
Addressed suggestions from newer version of ShellCheck.