Updates instrux in README, CONTRIBUTING and app notes

[diverdane]

Changes included:

• A VERSION text file is added to set the current published version
  for the Marketplace app.
• The publishedVersion field in the Marketplace schema.yaml is now
  passed in as a $TAG environment variable during builds of the Marketplace
  deployer (rather than being fixed) so that when we build and test/verify
  with new versions of conjur, deployer, nginx, etc., we're actually testing
  and verifying with the desired versions that were just built, not the
  pinned, published versions that have been previously pushed to GCR.
• The VERSION file is now set to 1.6.0, and the Conjur OSS version
  that is used by the Marketplace app is bumped to 1.6.0.
• The Jenkinsfile jobs will now read the VERSION file to determine tags.
  For master branch, contents of VERSION are used directly. For any
  other branch, the contents of VERSION are used with a suffix of
  -<short-commit-ref>.
• The version of Postgres used is changed from 9.4 to 10.1, since
  running with postgres:9.4 was failing. (Version 10.1 is the default
  version used in the conjur-oss helm charts).
• For testing and development, the build.sh script now allows for the
  setting of the issuer common name used in the Conjur CA certificate.
  This can be set via a CERTIFICATE_COMMON_NAME environment variable.
  This will make it easier to configure DNS A records or entries in
  the local /etc/hosts file for testing access to Conjur.
• README.md changes:
  • Corrects the manual helm install instructions so that the helm charts
    use the same image tags as used by the Marketplace application deployer.
  • Adds more details and corrects some inconsistencies in instructions
    for connecting to Conjur after helm installation.
• CONTRIBUTING.md changes:
  • Adds some steps for configuring and connecting to Conjur
  • Removed support for flat dockerhub registries, since this won't work
    with the way that schema.yaml expects a hierarchichal GCR registry.
• Marketplace application manifest:
  • Adds more details/clarifications on how to connect to Conjur
    and authenticate.

[sgnn7]

@diverdane Left a few comments

[sgnn7]

Ditto about sudo and noting that this could create duplicates and earlier entries will override newer ones. I think we may need a better CLI addition of a host.

[diverdane]

Changed this to first look for an existing entry for the common name. If an entry exists, it is overwritten with a new external IP with sed. Otherwise, a new entry is added to /etc/hosts.

[izgeri]

this line doesn't belong in the CHANGELOG, which should be used to describe user-facing changes to the project. is there a user impact of this change?

[diverdane]

Good point. There is no user impact of this change. The difficulty I have sometimes is keeping a crisp distinction between users and contributors... in that I conflate contributors as "users of our open source code". :)

[sgnn7]

@diverdane Getting really close!

[sgnn7]

@diverdane LGTM! Hopefully this will be all that's needed.

[sgnn7]

Edit: Looks like the build is failing though

[diverdane]

Edit: Looks like the build is failing though

Re-ran, and it passed. I don't know why the scan for fixable vulnerabilities failed before, as the scan results looked identical between passing and failing cases.