Use build:images instead of build:all and decouple build task from image-builds

Since the image builds take a long time and the release process is github based now, it's better to separate the tasks.
This allows to build the gem without the images.
Also name the task for building the images like release:images .

Author: larskanis

Rakefile

@@ -80,7 +80,7 @@ namespace :build do
     task platform => sdf do
       build_mri_images([platform], [local_platform], output: 'load')
     end
-    multitask :all => platform
+    multitask :images => platform
   end
 
   sdf = "tmp/docker/Dockerfile.jruby.#{rake_platform}"
@@ -89,7 +89,7 @@ namespace :build do
   task :jruby => sdf do
     build_jruby_images([local_platform], output: 'load')
   end
-  multitask :all => :jruby
+  multitask :images => :jruby
 
   all_mri_images = platforms.map(&:first)
   desc "Build images for all MRI platforms in parallel"
@@ -102,14 +102,12 @@ namespace :build do
   all_images = all_mri_images + ["jruby"]
   desc "Build images for all platforms in parallel"
   if ENV['RCD_USE_BUILDX_CACHE']
-    task :all => all_images
+    task :images => all_images
   else
-    multitask :all => all_images
+    multitask :images => all_images
   end
 end
 
-task :build => "build:all"
-
 namespace :release do
   host_pl = host_platforms.map(&:first).join(",")