deploy sets but does not use defaultRepo variable

[rofe]

Follow these steps (loosely based on getting-started):

1. hlx demo demo && cd demo
2. hlx build
3. git remote add origin <mytestprojectcode_repo_url>.git
4. hlx deploy --dirty --add=default

The resulting helix-config.yaml will look like this:

#
# helix configuration for local development
#
version: 1

definitions:
  defaults:
    - &defaultRepo "<mytestprojectcode_repo_url>.git"

strains:
  - name: default
    code: <mytestprojectcode_repo_url>.git#master
    content: <mytestprojectcode_repo_url>.git#master
    static: <mytestprojectcode_repo_url>.git/htdocs#master
    package: (...)

I would expect it to make use of the *defaultRepo variable, since it's being defined above.

[rofe]

Relates to #711

[tripodsan]

won't fix for helix 2. irrelevant for helix 3.