ign-tools additional commands should support relocatable install

[osrf-migration]

Original report (archived issue) by Silvio Traversaro (Bitbucket: traversaro).

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Summary

Currently the .yml files used by downstream projects contains the library_path field that contain an hardcoded location of the ruby script as it is in the build machine, see for example:

--- # Subcommands available inside ignition-transport.
format: 1.0.0
library_name: ignition-msgs
library_version: 1.0.0
library_path: E:/superinstaller/vcpkg/packages/ignition-msgs1_x64-windows/lib/ruby/ignition/cmdmsgs1
commands:
    - msg   : Print information about messages.
---

Ideally, ign-tools it should be able to encode the location of the ruby script relativly to the location of the .yml file.

Motivation

On a Windows system, it may occur that the installation location in the target system is different from the one of the build machine.

Describe alternatives you've considered

Always forcing users to install binary version of ignition libraries in the same prefix.
Alternativly, the .yml could provide some sort of "installation script" that would be run when installing them on a new machine, but in my experience such solution are more error-prone that a pure relocatable package.

Additional context

A nice description of the problem of the relocatable install (but in CMake context) can be found at https://cmake.org/cmake/help/v3.14/manual/cmake-packages.7.html#creating-relocatable-packages .

cc @seanyen-msft

[osrf-migration]

Original comment by Silvio Traversaro (Bitbucket: traversaro).

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• changed title from "ign-tools should support relocatable" to "ign-tools additional commands should support relocatable install"

[osrf-migration]

Original comment by Silvio Traversaro (Bitbucket: traversaro).

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• Edited issue description* changed kind from "bug" to "enhancement"