Docker-compose --build support

[jtanios]

This PR adds support to build the containers before starting the services.
Resolves #76

Also, there's an enhancement to the tests to make them run from anywhere, it doesn't have to be project root. This was an issue when running the tests from an IDE, like PyCharm.

[codecov-io]

Codecov Report

Merging #78 into master will increase coverage by 0.18%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #78      +/-   ##
==========================================
+ Coverage   84.94%   85.13%   +0.18%     
==========================================
  Files          19       19              
  Lines         392      397       +5     
  Branches       25       26       +1     
==========================================
+ Hits          333      338       +5     
  Misses         43       43              
  Partials       16       16              

Impacted Files	Coverage Δ
testcontainers/compose.py	100.00% <100.00%> (ø)

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[jtanios]

@tillahoffmann , would you like to review?

[tillahoffmann]

What does docker-compose do when --build is passed but the docker-compose.yml file doesn't contain any reference to a locally-built image?

[jtanios]

Good question!

I just tried it with the tests/docker-compose.yml and it had no effect; it worked exactly as it would without it.

[jtanios]

@tillahoffmann ☝️ is this good enough?

[tillahoffmann]

Closing for now as wontfix (see #83 for details), but thank you for the contribution!

This is a bit of a tricky one: it's somewhat easier to argue for supporting --build in docker compose because it's a single flag, whereas adding build functionality in general is probably beyond the scope of this library. Let's see whether this continues to be a need (as opposed to running docker compose --build prior to running the tests), and we can reconsider.