fix(zypp): Fixed moving libzypp target to /mnt (#1352)

## Problem

- Moving the libzypp target to `/mnt` (the target installed system)
happened too early, already in the "propose" step, it needs to happen
after partitioning the disk.
- The side effect of this is that mounting the `/mnt` partition can
shadow the libzypp cache so it could crash later. Also the next target
used after the product change would be the `/mnt` instead of the
`/run/agama/zypp`.

## Solution

- Move the target change to the "install" step

## Notes

- I found out that the `Pkg.SourceCacheCopyTo` call does not work
properly with target different than `/`. It always copies the data from
`/` ignoring the current target.
- It could copy some wrong data from the Live ISO to the target, as a
quick solution I have commented that out. I'll fix it later in a
separate PR.

## Testing

- Tested manually
- Updated unit tests

service/lib/agama/software/manager.rb

@@ -172,6 +172,11 @@ def propose
 
       # Installs the packages to the target system
       def install
+        # move the target from the Live ISO to the installed system (/mnt)
+        Yast::Pkg.TargetFinish
+        Yast::Pkg.TargetInitialize(Yast::Installation.destdir)
+        Yast::Pkg.TargetLoad
+
         steps = proposal.packages_count
         start_progress(steps)
         Callbacks::Progress.setup(steps, progress)
@@ -196,7 +201,10 @@ def finish
         progress.step(_("Writing repositories to the target system")) do
           Yast::Pkg.SourceSaveAll
           Yast::Pkg.TargetFinish
-          Yast::Pkg.SourceCacheCopyTo(Yast::Installation.destdir)
+          # FIXME: Pkg.SourceCacheCopyTo works correctly only from the inst-sys
+          # (original target "/"), it does not work correctly when using
+          # "chroot" /run/agama/zypp, it needs to be reimplemented :-(
+          # Yast::Pkg.SourceCacheCopyTo(Yast::Installation.destdir)
           registration.finish
         end
       end

service/lib/agama/software/proposal.rb

@@ -153,12 +153,8 @@ def languages=(value)
 
       # Initializes the target, closing the previous one
       def initialize_target
-        Yast::Pkg.TargetFinish # ensure that previous target is closed
-        Yast::Pkg.TargetInitialize(Yast::Installation.destdir)
-        Yast::Pkg.TargetLoad
-
         preferred, *additional = languages
-        Yast::Pkg.SetPackageLocale(preferred) if preferred
+        Yast::Pkg.SetPackageLocale(preferred || "")
         Yast::Pkg.SetAdditionalLocales(additional)
 
         Yast::Pkg.SetSolverFlags("ignoreAlreadyRecommended" => false, "onlyRequires" => false)

service/test/agama/software/manager_test.rb

@@ -83,6 +83,8 @@
 
   before do
     allow(Yast::Pkg).to receive(:TargetInitialize)
+    allow(Yast::Pkg).to receive(:TargetFinish)
+    allow(Yast::Pkg).to receive(:TargetLoad)
     allow(Yast::Pkg).to receive(:SourceSaveAll)
     allow(Yast::Pkg).to receive(:ImportGPGKey)
     # allow glob to work for other calls
@@ -339,14 +341,19 @@
         expect { subject.install }.to raise_error(RuntimeError)
       end
     end
+
+    it "moves the packaging target to /mnt" do
+      expect(Yast::Pkg).to receive(:TargetFinish)
+      expect(Yast::Pkg).to receive(:TargetInitialize).with(destdir)
+      expect(Yast::Pkg).to receive(:TargetLoad)
+      subject.install
+    end
   end
 
   describe "#finish" do
     it "releases the packaging system" do
       expect(Yast::Pkg).to receive(:SourceSaveAll)
       expect(Yast::Pkg).to receive(:TargetFinish)
-      expect(Yast::Pkg).to receive(:SourceCacheCopyTo)
-        .with(Yast::Installation.destdir)
 
       subject.finish
     end

service/test/agama/software/proposal_test.rb

@@ -45,13 +45,6 @@
   end
 
   describe "#calculate" do
-    it "initializes the packaging target" do
-      expect(Yast::Pkg).to receive(:TargetFinish)
-      expect(Yast::Pkg).to receive(:TargetInitialize).with(destdir)
-      expect(Yast::Pkg).to receive(:TargetLoad)
-      subject.calculate
-    end
-
     it "makes a proposal" do
       expect(Yast::Packages).to receive(:Proposal).and_return(result)
       expect(Yast::Pkg).to receive(:PkgSolve)