Changes the default when incremental build is enabled to use named
volumes instead of bindmounts.
The reason for this is, on Mac/Windows the bind mounts will go over the
shared fs, which is incredibly slow and itself uses lots of CPU.
Makes an incremental build on OSX go from ~40s to 10s.
To get the old behavior, can set `PKGCACHE_DIR=.go-pkg-cache`
Signed-off-by: Brian Goff <cpuguy83@gmail.com>
Upstream-commit: c9623d1b7619dfffe01fa47b4338637945c1a53f
Component: engine
655301f8a7