adds ceos support for extras

[sulrich]

overview

ceos allows some parameters to be overridden or additional options to be set by placing files within the flash directory. this PR adds support for a ceos-specific "extra" to copy user provided files into the flash directory on startup.

additionally, this PR sets the EBTA environment value to be "1" which is the preferred setting.

[hellt]

Hi @sulrich
since this operation seems to be a generic one, could it be named copy-to-flash instead of overrides?

PS. Also what is the benefit do you see when copying the files, instead of using binds?

[sulrich]

@hellt happy to change this to 'copy-to-flash' or something similarly generic.

wrt this vs. binds, it's really kind of a workflow and packaging thing. i tend to use this to inject the extras and then remove the "extras" from the topology file so that i can package this up for storage and restoration without having to worry about binds lurking around.

upon further reflection, it might make more sense to make this into something that's only used on initial setup.

[hellt]

Hi @sulrich check my changes in the latest commit

I have changed the node name to be ceos-copy-to-flash to avoid ambiguity and also added a step to resolve relative paths relative to the topology file and not the CWD. This is the common logic for paths in clab.

When you confirm that it works as you expected I will merge it

[sulrich]

builds clean, works correctly.

i'm good. thanks!