Tweaks to supplemental (non-core SDP) scripts p4u_env.sh, libcore.sh, template.sh:
* Fixed bug relying on $USER, which is not guaranteed to be defined,
preventing errors in unusual situations where it is not defined.
* Streamlined temp file management, adding new P4U_TMPDIR directory,
which is cleaned up automatically. It uses /dev/shm if available,
otherwise 'mktemp -d'.
* runCmd() and runRemoteCmd() now clean up temp files as they goes.
* Added new 'captureOutputFlag' parameter to runRemoteCmd(), with
similar semantics as with the same parameter in runCmd().
* Updated template.sh to illustrate new parameter in runRemoteCmd().