Interpret backslash escapes for RCON_CMDS

[quulah]

Uses echo -e to interpret any included backslash escapes within RCON_CMDS_. Such as the literal \n newlines.

Fixes #3007

[quulah]

printf might be more portable. It seems echo has varying implementations across shells and OS's. But this being a container and we have the /bin/bash shebang, I guess we can rely -e on being there.

[itzg]

printf might be more portable. It seems echo has varying implementations across shells and OS's. But this being a container and we have the /bin/bash shebang, I guess we can rely -e on being there.

Yeah, I had seen similar comments about portability, but yes, as you said, the container gives us a guaranteed bash implementation.

[itzg]

Thanks for the quick turn around! I'll merge this after the PR test finishes.