DVPL-3678: splunklib.searchcommands | validators.File should open files with path names relative to $SPLUNK_HOME/var/run/splunk

Also added stack trace to each search command type's _execute method for improved feedback.

Signed-off-by: David Noble <dnoble@splunk.com>
Merge branch 'develop' of https://github.com/splunk/splunk-sdk-python into develop