remote: Put tests behind io-testsuite flag

Disabled by default since it requires `nix-daemon` binary
and Linux namespaces support.

For development this can be enabled by

```
cabal configure --flag=io-testsuite
```

or by adding

```
flags: +io-testsuite
```

to `cabal.project.local`

Enabled by `callCabal2nixWithOptions` in `overlay.nix` so
it is tested by `nix-build` and `nix-shell` brings all
test dependencies.

This is fine on NixOS where `build-tool-depends: nix:nix-daemon` works
and we have namespaces supported.

hnix-store-remote/hnix-store-remote.cabal

@@ -13,6 +13,13 @@ build-type:          Simple
 extra-source-files:  ChangeLog.md, README.md
 cabal-version:       >=1.10
 
+flag io-testsuite
+  default:
+    False
+  description:
+    Enable testsuite, which requires external
+    binaries and Linux namespace support.
+
 library
   exposed-modules:     System.Nix.Store.Remote
                      , System.Nix.Store.Remote.Binary
@@ -45,6 +52,11 @@ library
   ghc-options:         -Wall
 
 test-suite hnix-store-remote-tests
+   if !flag(io-testsuite)
+     buildable: False
+
+   build-tool-depends: nix:nix-daemon
+
    ghc-options:       -rtsopts -fprof-auto
    type:              exitcode-stdio-1.0
    main-is:           Driver.hs

overlay.nix

@@ -2,5 +2,5 @@ huper: helf: {
   hnix-store-core =
     helf.callCabal2nix "hnix-store-core" ./hnix-store-core {};
   hnix-store-remote =
-    helf.callCabal2nix "hnix-store-remote" ./hnix-store-remote {};
+    helf.callCabal2nixWithOptions "hnix-store-remote" ./hnix-store-remote "-fio-testsuite" {};
 }