images.build failing on container build output

[datwiz]

The ImageCollection.build() method parses the docker build output to extract the name of the image being built by looking for the string "Successfully built {sha256}". Some commands in a Dockerfile can also produce this string causing the build() method to return early with an incorrect image name.

Example output from a RUN pip install cffi command:

 ...
Building wheels for collected packages: cffi, pycparser
  Running setup.py bdist_wheel for cffi
  Stored in directory: /root/.cache/pip/wheels/ea/df/5c/7d11cd4eec7b94be3b0ec4ed0076e0f38846a22c7200576149
  Running setup.py bdist_wheel for pycparser
  Stored in directory: /root/.cache/pip/wheels/bc/07/7e/cd81c0b23417ebaed9eb2584c00bd539871d5309a7a2324953
Successfully built cffi pycparser
...

A partial fix is to make the regex used to search for the string more restrictive by adding start and end anchors. This can still result in some false positives.
A more complete fix only checks the last line of output for the "Success..." string.
PR in progress.

docker==2.3.0
docker-pycreds==0.2.1
Python 2.7.5
Client:
 Version:         1.12.6
 API version:     1.24
 Package version: docker-common-1.12.6-16.el7.x86_64
 Go version:      go1.7.4
 Git commit:      3a094bd/1.12.6
 Built:           Tue Mar 21 13:30:59 2017
 OS/Arch:         linux/amd64

Server:
 Version:         17.03.1-ce
 API version:     1.27
 Package version: 
 Go version:      go1.7.5
 Git commit:      c6d412e
 Built:           Fri Mar 24 00:00:50 2017
 OS/Arch:         linux/amd64