gnu: docker: Optimize substitution macros.

gnu: docker: Optimize substitution macros.

This change halves the time needed to patch the paths.

* gnu/packages/docker.scm (docker)[phases]{patch-paths}: Allow passing
multiple SOURCE-TEXT, PACKAGE and RELATIVE-PATH tuples so that the rewrite
rules can be generated and processed by a single use of the SUBSTITUTE*
macro.  Rename SUBSTITUTE-LOOKPATH to SUBSTITUTE-LOOKPATH* and
substitute-Command to SUBSTITUTE-COMMAND* to denote the change.  Adapt the
uses of SUBSTITUTE-LOOKPATH* and SUBSTITUTE-COMMAND*.