Fix space-suffix option

[matthew-reynolds]

Addresses #545

From the docs, the catkin config --space-suffix argument should set the "Suffix for build, devel, and install space if they are not otherwise explicitly set." However, currently, the default values for each of these spaces are considered "explicitly set". This means that, except for an extremely narrow window when first initializing a workspace, the --space-suffix argument is always useless.

This PR allows --space-suffix to affect spaces whose values are either not set or are set to the default values. This brings the tool back in line with how it used to behave.

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Aside: The documentation says that this affects the build, devel, and install spaces, but the code is implemented such that it affects the build, devel, install, and log spaces. I assume the code is correct and the documentation is out of date, but I'd like to get confirmation on which is prefered so that I can update the code/documentation accordingly.

[matthew-reynolds]

Some more details:

Whenever a context is saved, it writes all of its space values to the profile's config.yaml file. This includes all space values, even if the space values are default. Therefore, the only time when the --space-suffix tool can have any effect is immediately after initializing a workspace before the context is saved.

Importantly, contexts are saved in a lot of different cases (whenever catkin profile add, catkin profile rename, catkin build --save-config, or any catkin config commands are run), meaning the --space-suffix tool will almost immediately be useless once you start using the workspace. Even just running catkin config to read back the config summary or adding a new profile will save the context and write the default values to the config file, rendering the --space-suffix argument useless.

[mikepurvis]

Thanks for figuring this out and addressing it.