remote-add: Add --set=KEY=VALUE option

This can be used to add a remote and set e.g. tls-permissive=true, or
gpgverify=false.

tests/test-basic.sh

@@ -299,3 +299,9 @@ ${CMD_PREFIX} ostree --repo=repo2 init
 ${CMD_PREFIX} ostree --repo=repo2 pull-local repo
 echo "ok pull-local after commit metadata"
 
+cd ${test_tmpdir}
+${CMD_PREFIX} ostree --repo=repo remote --set=tls-permissive=true add aremote http://remote.example.com/repo testos/buildmaster/x86_64-runtime
+assert_file_has_content repo/config 'tls-permissive=true'
+assert_file_has_content repo/config 'remote\.example\.com'
+echo "ok remote add with set"
+