Move migrate binary to /usr/local/bin in Dockerfile

[jace-ys]

Move the migrate binary to /usr/local/bin in Dockerfile, so it
can be invoked from anywhere - this makes it easier to write
entrypoint scripts that call migrate that can can be used
consistently both locally and in Docker containers.

[jace-ys]

This PR addresses issue #304. I couldn't see anywhere else in the code / documentation that I needed to modify, so please point out if I missed something!

[coveralls]

Pull Request Test Coverage Report for Build 722

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 53.191%

---

Totals
Change from base Build 716:	0.0%
Covered Lines:	2559
Relevant Lines:	4811

---

💛 - Coveralls

[jace-ys]

I just realised that this breaks people's assumption of where the binary exists, which might not be backwards compatible with scripts / code that depend on the binary existing as /migrate (not sure how big that audience is).

To preserve backwards compatibility, what we could do instead:

1. COPY the binary to both /migrate AND /usr/local/bin/migrate
2. COPY the binary to /usr/local/bin/migrate and create a symlink to /migrate

What do you guys think is the preferred option here?

[dhui]

Thanks for the PR!

To preserve backwards compatibility, what we could do instead:

1. COPY the binary to both /migrate AND /usr/local/bin/migrate
2. COPY the binary to /usr/local/bin/migrate and create a symlink to /migrate

Use a symlink to reduce image size

[jace-ys]

Use a symlink to reduce image size

Have updated the PR to now create the symlink! 👍