Extend --tag=branch which tags image with branch and sha

[martindekov]

With this commit the --tag is extended to include branch argument
which tags image not only with sha but branch-sha

Signed-off-by: Martin Dekov (VMware) mdekov@vmware.com

Extend the --tag with branch feature which tags image with branch and sha.

Description

Added checks to see the --tag argument if its branch it calls not only
GetGitSha, but also new function which checks the branch we are in.
If we are not in a repo it fails and if we are in a repo it gets the branch
and adds it to the image name name.

Motivation and Context

• I have raised an issue to propose this change (required)

This references #463.

How Has This Been Tested?

Tested by building pushing and deploying image with my change.
Example pushed images are found in this docker hub repo:
https://hub.docker.com/r/martindekov/gofun/tags/
Adding image:<example name>:<example replacement of latest>
to check if latest will be appended in case the replacement exists.
Tried do build when not in a git repo with --tag=branch it returned error
2018/07/24 02:09:14 ERROR - Could not execute command: [docker build -t martindekov/gofun:0.2-fatal: not a git repository (or any of the parent directories): .git-fatal: not a git repository (or any of the parent directories): .git .]

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I've read the CONTRIBUTION guide
• I have signed-off my commits with git commit -s
• I have added tests to cover my changes.
• All new and existing tests passed.

[alexellis]

Derek set milestone: 0.6.16

[alexellis]

LGTM