get emulator binary as part of image build

[edaniszewski]

Right now, the binary for the emulator plugin that is built-in to some synse server images for convenience get here by:

• building a linux distribution of the emulator plugin
• copying it into the synse-server emulator directory
• rebuilding the synse-server image to include it

Likely, a better approach would be to not have the emulator plugin binary in this repo at all, but instead download it into the image on build via GitHub releases.

[edaniszewski]

Tried doing this a variety of ways, but no success. For whatever reason when I install it (either via cURL or via dockerfile ADD, when I chmod and place the binary in the correct place (verified w/ ls that is is actually there) and then run the container w/ emulator enabled, I see:

bin/synse.sh: line 82: ./emulator: No such file or directory

I'll revisit this later, just posting this in case anyone else has seen this before

[edaniszewski]

the reason I was having trouble with this is related to: https://stackoverflow.com/a/35613430/8162473

Namely, when building the linux_amd64 variant, its not linked to libc, not muslc which the alpine image uses. there is a fairly simple fix via the SO post linked above, but maybe we will want to have a muslc build of the emulator as well?