Improve Dockerfile parsing

[TrevCraw]

Currently, the implementation for parsing the Dockerfile COPY lines and WAR file lines is limited in the scenarios it covers. The following are scenarios we should consider handling in the future:

• Variable substitution for WAR file name/path or other COPY line file/path (this could be using ENV variable or other kinds)
• Wild cards in the WAR file name/path or other COPY line file name/path
• Multiple <src> to one <dest> (covered by Handle Dockerfiles with multiline and comments ci.common#158)
• Multi-line COPY commands with line breaks (covered by Handle Dockerfiles with multiline and comments ci.common#158)
• Spaces in the WAR file or COPY paths (Handle spaces in Dockerfile's war file copy path #856) [edit: I'm not sure it is easy to use spaces. One way is to hide them in variables e.g. ENV my_cat="big guy" and another is to use JSON format e.g. copy ["foo foo" , "bar"] ]
• Relative path to WORKDIR
• Multi-stage builds, how to handle a file being copied from another image? (Support auto-generated Dockerfile from Transformation Advisor #1073)
• How should we handle permissions specified by the COPY command for mounting? Is it possible to handle this?
• JSON format e.g. copy ["src/main/liberty/config/server.xml" , "/config/"]
• Any other bad syntax we need to handle?

[yeekangc]

Consider if there is a framework or library that we should use and/or contribute to for the purposes here.