This removes the ability to support http proxy directly, but fixes issues where users may not
be using exactly the same herokuish as we expect.
Closes#2828
[ci skip]
This allows users to override - at a top-level - the DOKKU_ROOT, DOKKU_LIB_ROOT, and other
configuration variables. If specified, this should begin to enable users to move their
Dokku installations to mounted drives.
Note that items installed from packages may not respect these paths, so further work may be in order.
Closes#2958
Herokuish update fails if existing herokuish is used by other containers,
using docker build --pull will force to update also the base image.
Setting up herokuish (0.3.28) ...
Removing old herokuish image
Failed to remove image (gliderlabs/herokuish): Error response from daemon: conflict: unable to remove repository reference "gliderlabs/herokuish" (must force) - container dbf2298ab5a5 is using its referenced image 7d4a8d661476
Importing herokuish into docker (around 5 minutes)
