This PR adds support for 'AS' names in Dockerfiles. e.g. `FROM node:8 AS base`. It also adds logic to detect and ignore - for now - any image sources from custom registries.
Renovate will now check ignorePaths values for either (a) a string match, or (b) glob pattern. e.g. a string of ‘node_modules/‘ will ignore ‘node_modules/foo/package.json’ and ‘backend/node_modules/foo/package.json’ but it will also ignore ‘not_node_modules/foo/package.json` too. Therefore a blog pattern of `**/node_modules/**` is superior.
Closes#1054
BREAKING CHANGE: ignorePaths now supports globs and may match more than before, but that’s probably a good thing.
