qemublocktest: Add JSON->JSON test cases for block device backends

Add testing of the interpretation of the JSON pseudo-protocol backing
store into JSON structs for blockdev. This will be used to test JSON
pseudo-URIs used by libguestfs while actually also validating the output
against the QMP schema. Since libguestfs uses obsolete/undocumented
values the outputs will differ and a benefit is that modern output is
used now.

The example test case covers the fields and values used by libguestfs
when using the https driver.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>

tests/qemublocktestdata/jsontojson/curl-libguestfs-in.json

@@ -0,0 +1 @@
+json:{"file.driver":"https","file.url":"https://test.host/whatever.img","file.timeout":2000,"file.readahead":65536,"file.sslverify":"off","file.cookie":"some_cookie=\"some_value_or_whatever\""}

tests/qemublocktestdata/jsontojson/curl-libguestfs-out.json

@@ -0,0 +1,9 @@
+{
+  "driver": "https",
+  "url": "https://test.host:443/whatever.img",
+  "sslverify": false,
+  "timeout": 2000,
+  "readahead": 65536,
+  "auto-read-only": true,
+  "discard": "unmap"
+}