nixops: add checkPhase with a smoke test

This can detect (python) import errors introduced by dependency updates.

pkgs/tools/package-management/nixops/generic.nix

@@ -1,4 +1,4 @@
-{ lib, python2Packages, libxslt, docbook_xsl_ns, openssh
+{ lib, python2Packages, libxslt, docbook_xsl_ns, openssh, cacert
 # version args
 , src, version
 }:
@@ -29,7 +29,13 @@ python2Packages.buildPythonApplication {
       typing
     ];
 
-  doCheck = false;
+  checkPhase =
+  # Ensure, that there are no (python) import errors
+  ''
+    SSL_CERT_FILE=${cacert}/etc/ssl/certs/ca-bundle.crt \
+    HOME=$(pwd) \
+      $out/bin/nixops --version
+  '';
 
   postInstall = ''
     make -C doc/manual install nixops.1 docbookxsl=${docbook_xsl_ns}/xml/xsl/docbook \