Revise hard-coded paths to the engineering_tools deploy directory from within engineering_tools

[ZLLentz]

Expected Behavior

All scripts in engineering_tools that need to run another script in engineering_tools should run the script in the same release directory, so that we can isolate version-specific behavior and test/deploy more easily.

Current Behavior

Some scripts reference the specific release directory directly:

engineering_tools/scripts/set_gem_timing

Line 31 in 953c167

IMGR_CMD_PATH="/reg/g/pcds/engineering_tools/latest-released/scripts/imgr"

Possible Solution

Use any of the various bash-isms for getting the current directory of a shell script.

Context

#204 (comment)